C1139 Social Insects. Diversity & Systematics. Lecture 5
Biodiversity and systematics: the different groups of social insects
Aims
1. To provide a systematic overview of eusocial insects emphasizing the multiple origins of eusociality.
2. To provide additional basic information on the different groups of social insects.
Objectives
1. To learn about the multiple origins of eusociality, and how this leads to the conclusion that many social
traits have convergently evolved.
2. To have a basic awareness and knowledge of the different lineages of social insect, their relationship to
each other and the main taxa within each.
The Big Picture
Eusociality has evolved many times in insects. Once in the termites, formerly considered an order (Isoptera)
but now considered a family within the Blattaria (cockroaches) and approximately 9 times in the
Hymenoptera. Eusocial species are found only within the aculeate Hymenoptera, not throughout the whole
order. A single origin gave rise to all ants, three to eusocial wasps, and multiple origins to the eusocial bees.
To understand social insects it is essential to have some knowledge of their systematics. This will
tell you, for example, whether two eusocial genera are closely related members of the same eusocial lineage
(e.g., Vespula and Dolichovespula wasps), more distant members of the same lineage (e.g., Polistes and
Vespula wasps; Formica and Atta ants), or members of different eusocial lineages (e.g., ants and honey
bees; ants and Vespidae wasps; Lasioglossum bees and honey bees). If two species belong to different
eusocial lineages and both have a eusocial trait in common, such as having worker policing or
morphologically distinct queens and workers or foraging communication, then these traits must have
evolved convergently because they were not found in the non-eusocial common ancestor. (The common
ancestor of any two species that belong to different eusocial lineages was non-eusocial. For example, the
common ancestor of honey bees and ants was a non-eusocial aculeate wasp.)
In total there are about 15,000 known species of eusocial insects. The actual number is almost
certainly more than 20,000. The different origins of eusociality in insects vary greatly in the size of the
adaptive radiation that followed. The ant radiation is the largest with c. 12,000 known species. Second come
the termites with several thousand. Third are the Apidae bees with over one thousand. At the other extreme,
two origins have just a single species including the Sphecidae wasp Microstigmus comes and the bark beetle
Australoplatypus incompertus. The two eusocial mole rats, the naked mole rat and the Damaraland mole rat,
are also indpependent single-species origins of eusociality, even though both are within mole rats
(Mammalia: Rodentia: Bathyergidae). There are also multiple eusocial origins within the Halictidae bees,
aphids, and snapping shrimp.
Understanding some of the key features of eusocial insect systematics (= taxonomic arrangement
according to phylogeny, and other information) will greatly help you to understand social insect evolution
and diversity. It will also help you to organize many facts that you learn into a convenient framework.
Some references are given in the slides and below. A recent book (Grimaldi D, Engel M. 2005. The
evolution of insects. Harvard University Press) is a detailed treatment of insect diversity and systematics and
has phylogenies of all the groups discussed. But be aware that systematists do not always agree!
Isoptera (termites)
Termites are social cockroaches. Formerly they were considered to be a whole insect order, the Isoptera.
However, recent research indicates that the termites are nested within the cockroaches (Blattaria),
phylogenetically speaking, and so are best thought of as a family not an order (Inward et al. 2007).
(Similarly, the ants are a single family of eusocial species nested within the Hymenoptera Aculeata.)
Termites are diploid hemimetabolous insects. All species are eusocial and there are no social parasites, as
has evolved repeatedly within eusocial Hymenoptera. There are approximately 2300 species. They are found
worldwide and are most diverse in the humid tropics, maximally in equatorial West Africa (Cameroons).
There are no species living in Britain and only a few in Europe. Termites are the oldest eusocial group and
originated c. 180 million years ago. This is a long time but is some 200 million years after insects evolved.
All species feed on dead plant material or organic matter in the soil. All have symbiotic micro-organisms to
help them digest cellulose. In most species the symbionts (protozoa, bacteria) are held in the termite’s gut,
which is a miniature bio-digester. Some “higher” termites have evolved the ability to cultivate fungi in
gardens within the nest. The fungi digest the plant material and are eaten by the termites. Fungus farming in
termites is found only in the old world (Africa, Asia). Fungus farming has also evolved in the Attini ants
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C1139 Social Insects. Diversity & Systematics. Lecture 5
(probably in South America) which include the leafcutter ants Atta and Acromyrmex and several other
genera, and is found only in America. This is an example of convergent evolution.
Inward, D., Beccaloni, G. Eggleton, P. 2007. Death of an order: a comprehensive molecular phylogenetic study
confirms that termites are eusocial cockroaches. Biology Letters 3: 331-335.
Hymenoptera
Hymenoptera are haplodiploid holometabolous insects. With over 115,000 described species the
Hymenoptera are one of the four largest insect orders. The other of the big 4 orders are the Coleoptera
(beetles), Diptera (flies) and Lepidoptera (moths & butterflies). When fully described the Hymenoptera may
prove to be the most diverse insect order. Approximately 10% of hymenopteran species are eusocial. All
ants are eusocial or are workerless social parasites. Most bees are not eusocial. Most wasps are not eusocial.
Bees are hairy wasps. Ants are wingless eusocial wasps.
Hymenoptera systematics
The Hymenoptera include the sawflies and woodwasps, parasitic wasps, wasps, ants and bees. They are
divides into three groups.
Symphyta: sawflies, wood wasps etc., 6000 species. An ecologically and economically important group of
herbivorous insects, including many that are pests of forestry and agriculture. They have a serrated
(sawflies) or pointed (woodwasps) ovipositor. None are eusocial. The larvae of some sawflies do aggregate
for defence, and may also all be siblings arising from a single batch of eggs.
Apocrita: parasitoid wasps, 55,000 species. An ecologically and economically important group of insects
that kill other insects by laying eggs on or in them with a pointed ovipositor, which also injects venom.
None are eusocial.
Aculeata: parasitoids and predatory wasps, ants, bees, eusocial wasps, 54,000 species. Use of the ovipositor
solely as a sting is the outstanding aculeate synapomorphy (shared derived character). It is not used to lay
eggs. Eggs emerge at the base of the ovipositor. All the eusocial Hymenoptera occur within the Aculeata.
Why is this so? Almost certainly because many solitary aculeates are nest builders. Females build a nest in
which to rear their brood. Brood are fed on prey (wasps) or pollen/nectar (bees). The nest is potentially
reusable and is also a location where kin occur. Both favour helping. If haplodiploidy alone were the main
cause of eusociality in the Hymenoptera, then eusocial species should not be confined to the Aculeata. There
are 3 superfamilies within the Aculeata. Eusocial species occur in two of these.
Chrysidoidea (or Bethyloidea): Parasitoid wasps. There are several families including the Chrysididae,
the jewel wasps (cute green shiny wasps). No eusocial species.
Apoidea (or Spheoidea): bees (6 main families, c. 20,000 species, c. 2,000 eusocial, c. 5 eusocial
origins) and sphecid wasps (7,700 species, 1 eusocial origin, 1 eusocial species currently known)
Vespoidea: several families including Vespidae wasps (potter wasps [non eusocial], hover wasps, paper
wasps, yellowjackers & hornets [eusocial, 1 eusocial origin, c. 1200 eusocial species]); ants (Formicidae,
c. 12,000 known species, 1 eusocial origin, all eusocial or workerless social parasites).
Brief sketches of the eusocial Hymenoptera
Ants (Formicidae)
The most diverse group of eusocial insects. Mature colonies range from 10 to 22 million individuals. Most
are founded by a lone queen, some by colony fission. Ants are basically ground-dwelling predatory wasps
but have diversified to become seed gatherers, fungus gardeners etc. Ants originated about 120 million years
ago. Ants have the largest colonies in the Hymenoptera, up to 22 million workers in African army ants
(Dorylus spp.) and the most complex symbiotic interactions (fungus growing, aphid farming, living within
plants). Workers are wingless but queens and males are usually winged. In some species workers show
complex morphological differences. There is a wide diversity of social parasitisms including slave makers
and workerless parasites. Unfortunately, there are no solitary ants to study.
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C1139 Social Insects. Diversity & Systematics. Lecture 5
There are numerous subfamilies. British ants are mainly Myrmicinae (e.g., Myrmica rubra the red
ant) and Formicinae (e.g., the wood ants Formica and the black garden ant Lasius niger). Formicine ants
have lost their sting, but retain the venom gland and can produce and release formic acid and other defensive
and offensive chemicals. Below is some information about various subfamilies. It is not necessary to learn
all the names. One immediate take-home message is that the genera with large colonies and elaborate social
systems (e.g., Atta, Eciton, Oecophylla) are not closely related. Large complex societies, therefore, have
evolved multiple times in the ants as well as in termites, Apidae bees and Vespidae wasps.
Ponerinae: In this subfamily workers of many species have not lost the ability to mate. In some
species the queen morphological caste has been secondarily lost and the queen role is taken by one or more
mated workers, sometimes known as "gamergates". The gamergates are to all intents and purposes queens,
but they are not of the queen caste. In some species colonies are founded by a queen, who is replaced when
she dies by gamergate. Colonies in the same population can thus be headed by a queen or by gamergates.
Army ants are several subfamilies close to the Ponerinae: Dorylinae, Ecitoninae, Leptanillinae.
The Formicinae include weaver ants (Oecophylla), wood ants (Formica), carpenter ants
(Camponotus), garden ants (Lasius).
The Myrmicinae include the fungus-growing ants (Atta, Acromyrmex), fire ants (Solenopsis), and
also many other important genera including Leptothorax and Pheidole.
Bees
Bees are a single lineage of wasps that underwent an adaptive radiation based on the invention of eating
pollen instead of prey. They are more hairy than normal aculeate wasps. The hairs are branched
(“plumose”). This helps pollen to stick to the bee’s body. Eusocial bees are pollen and nectar gatherers like
the non-eusocial bees. Within the eusocial bees, social parasites have evolved many times, including twice
in bumble bees, in sweat bees (Halictidae) and in allodapine bees, but not in stingless bees (Meliponinae) or
honey bees. A few stingless bee species are robbers. They pillage nests of other species of stingless bees for
their stored food. A few stingless bees collect carrion in place of pollen as a protein source and fruit in place
of nectar. Eusociality has evolved multiple times in the bees. Michener (1974) placed the bees in 9 families.
Eusocial bees are found in only three of these families (Apidae, Halictidae, and Anthophoridae). Only in the
honey bees and stingless bees do colonies become massive, with up to 60,000 in a large honey bee colony
(Apis mellifera) and perhaps 200,000 in some stingless bees. But most stingless bees have much smaller
colonies.
Bees: Apidae. Females in this family collect pollen using the familiar pollen basket (corbicula) on the tibia
of the hind leg. (For this reason they are sometimes referred to collectively as the corbiculate bees.) There
are four subfamilies (or tribes) within the Apidae. Almost certainly there is a single origin of eusociality
within the Apidae (Thompson & Oldroyd 2004). Apidae eusocial bees are extremely abundant worldwide
and are the main pollinating animals. Their nests are perennial (i.e., can live for more than one year ) (honey
bees, stingless bees, a few tropical bumble bees) or annual (most bumble bees). Fossil worker stingless bees
in cretaceous New Jersey amber show that eusociality evolved at least 70 million years ago in the Apidae.
Apinae
(honey bees)
Meliponinae
(stingless bees)
Bombinae
(bumble bees)
Euglossinae
(orchid bees)
eusocial; native to Asia, Africa & Europe and introduced to other continents
9 species, Asia only, except A. mellifera (Africa, Europe, Middle East)
maximum colony size ranging from 10,000 to 100,000
perennial swarm-founded colonies
eusocial; native to all continents except Europe; tropical, a few sub-tropical
c. 1000 species; most diverse in tropical America
maximum colony size ranging from c. 100 to more than 100,000
perennial swarm-founded colonies
eusocial: native to all continents except Australia; mostly temperate
c. 300 species
maximum colony size ranging from c. 10 to 1000
annual colonies founded by a lone queen; perennial in a few tropical species
solitary or communal: large bees, often metallic; tropical America only
Thompson G. J, Oldroyd, B. P. 2004. Evaluating alternative hypotheses for the origin of eusociality in corbiculate bees.
Molecular Phylogenetics & Evolution 33:452-456.
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C1139 Social Insects. Diversity & Systematics. Lecture 5
Bees: Halictidae. Often called sweat bees. Mostly ground nesting bees with annual nests. Many noneusocial species. There are four subfamilies. Eusociality has evolved in two of these subfamilies, three times
in total. In the three eusocial lineages combined there are almost 1000 eusocial species. It appears that
eusociality evolved only c. 22 million years ago in all three eusocial sweat bee lineages at the same time
during a period of warmer temperatures. There have been many reversions to solitary nesting (=
subsociality). That is, eusociality has frequently been lost. Some of these reversions are associated with a
switch from polylecty (wide range of plants visited) to oligolecty (small range of plants visited), which
probably leads to a short active season with a single, solitary, generation per year. Reversion is possible as
in eusocial sweat bees there is no morphological queen caste and queens can found nests on their own.
Conversely, it would be almost impossible for honey bees and stingless bees to revert to solitary living
because no one honey bee or stingless bee can nest on its own.
Rophitinae
Nomiinae
Nomioidinae
Halictinae
Augochlorini
Halictini
subfamily without social species
subfamily without social species
subfamily without eusocial species
subfamily with al most 1000 eusocial species, 3 origins of eusociality
maximum colony size ranging from less than 10 to more than 1000
colonies founded by a single female or association of a few females
tribe in which eusociality has evolved once; 1 reversion to solitary
c. 500 species, c. 140 eusocial, Augochlora & Augochlorela
tribe in which eusocialty has evolved twice; 9-11 reversions to solitary
Lasioglossum: 1268 species in total, c. 500 eusocial; 5 reversions
Halictus: 217 species in total, most eusocial; 4-6 reversions
Danforth, B. N. 2002. Evolution of sociality in a primitively eusocial lineage of bees. Proceedings of the National
Academy of Sciences of the USA 99: 286-290.
Bees: Anthophoridae. This is a large family of bees. Eusocial species occur in two subfamilies. A third
subfamily is comprised of parasites. Very little research has been done on the eusocial allodapines. Most of
what has been done is from Australia. Colonies are small.
Nomadinae
Xylocopinae
Ceratinae
all are parasitic
mostly non-eusocial
some eusocial species in the Allodapini (only in Asia, Africa, Australia)
possibly, there is occasional eusociality in some large carpenter bees, Xylocopa
Probably 1 origin of eusociality, eusocial species in several genera
Dwarf carpenter bees; mostly non-eusocial
One origin of eusociality with 3-4 species that occasionally have nests with helpers
Wasps
Wasps: Vespidae. All eusocial wasps, except for one species, are Vespidae. Not all Vespidae are eusocial.
All the eusocial species occur in three Vespidae subfamilies, and all species in these subfamilies are
eusocial or social parasites. Nests are both annual and perennial (Polistinae: Epiponini). Until recently it
was thought that there was a single of origin of eusociality, but now it is thought that the hover wasps,
Stenogastrinae, are not closely related to the other eusocial Vespidae species and evolved eusociality
independently (Hines et al. 2007).
Hines, H. M., Hunt, J. H., O’Connor, T. K., Gillespie, J. J., & Cameron,S. A. 2007. Multigene phylogeny reveals
eusociality evolved twice invespid wasps. Proceedings of the National Academy of Sciences USA 104: 3295-3299.
Stenogastrinae
Euparaginae
Masarinae
Eumeninae
Polistinae
hover wasps; eusocial; S.E. Asia only
nest made of paper or mud
solitary nest builders
honey wasps; solitary nest builders
potter wasps; solitary; solitary nest builders
mud nest is provisioned with paralyzed insect prey
paper wasps: eusocial; worldwide temperate and tropical but not Britain
Polistes, Mischocyttarus small colonies ranging from 10 to 100
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C1139 Social Insects. Diversity & Systematics. Lecture 5
Epiponini
Vespinae
Nest founded by a single female or foundress association of a few females
tropical American tribe of Polistinae with large swarm-founded nests
maximum colony size ranging from c. 100 to 1000,000, nest in envelope
maximum colony size ranging from a few 10s to more than 10,000
colonies founded by a single female; nest enclosed in an envelope
hornets (Vespa), Provespa, yellowjackets (Dolichovespula, Vespula)
Dolichovespula and Vespula: temperate, native Europe, N. America Asia.
Vespa: native to Europe, Asia, temperate and tropical
Provespa: tropical S.E. Asia only
Wasps: Sphecidae. The Sphecidae are the sister group to the bees, and together make up the Apoidea. One
species, Microstigmus comes, is eusocial. This is a diminutive wasp which builds a nest of plant hairs under
palm fronds and is found in Costa Rica. Maximum colony size is a few 10s of wasps. Research in Brazil by
Jeremy Field of Sussex University and his students is investigating whether other species of Microstigmus
are eusocial.
Number of independent origins of eusociality in Isoptera and Hymenoptera
Compiled by F. Ratnieks from various sources
No. eusocial origins
No. eusocial species
Eusocial species in Britain?
Isoptera (termites)
1
2300
no
Hymenoptera
c.9
Ants
1
Formicidae
1
12000
yes
Bees
c.5
Halictidae
3
900
yes
Anthophoridae
1?
50?
no (non-eusocial species only)
Apidae
1
1300
yes
Wasps
2
Vespidae
2
1200
yes
Sphecidae
1
1
no (non-eusocial species only)
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C1139 Social Insects. Diversity & Systematics. Lecture 5
Some key taxon and common names to learn
Learning about social insects requires learning the names of many taxa, at hierarchical levels from order to species.
There is no definitive list for the beginner. The list below provides some of the key species, genera and higher taxa that
will often be discussed in this course. You have photos of most of them, and many are familiar insects. Common names
are given in brackets. Note the following about names:
Genus, species and subspecies names should be italicized, or underlined when hand written.
Example: Apis mellifera mellifera (honey bee) subspecies native to Britain; Vespa crabro (the hornet)
Names at all taxonomic levels above genus are not italicized but begin with a capital letter.
Examples: Animalia, Arthropoda, Insecta, Hymenoptera, Apidae, Vespinae
If you use a higher taxonomic level name in other than its exact scientific form it is not capitalized.
Examples: British animals, common arthropods, social insects, subsocial hymenopterans, apid bees, vespine wasps
Do not capitalize common names unless they contain a proper name
Japanese giant hornet, honey bee, common wasp, hornet, pharaoh’s ant
The family level can be confusing as there are four levels. But this can actually make things easier to understand. If the
lecturer refers to Apidae bees then to Apinae bees, you know that the Apinae are a subgroup of Apidae. One source of
confusion is that a taxon can be given different hierarchical levels by different researchers (e.g., Apinae called Apini).
Superfamily: ends in –oidea; examples Apoidea
Family: ends in –idae; examples Halictidae, Anthophoridae, Apidae
Subfamily: ends in –inae; examples Apinae, Bombinae, Meliponinae
Tribe: ends in –ini; example Attini
Order: Isoptera (termites) name used for termites when they were considered an order on their own
Family: Termitidae name used for termites as a family of cockroaches, Blattaria.
Order: Hymenoptera (sawflies, woodwasps, parasitoid/parasitic wasps, wasps, yellowjackets, hornets, bees, ants)
Suborders: Symphyta, Apocrita, Aculeata
Bees
Halictidae (sweat bees)
Halictinae, subfamily containing eusocial species
Augochlorinae, subfamily containing eusocial species
Anthophoridae (carpenter bees, allodapine bees)
Allodapini: taxon with majority of anthophorid eusocial bees, small colonies
Apidae
Bombinae (bumble bees)
Bombus (bumble bees), all bumble bees are in this genus
Apinae (honey bees)
Apis (honey bees) all honey bees are in this genus; Apis mellifera (the honey bee; hive bee; western hive bee)
Meliponinae (stingless bees)
Melipona, one of the many genera of stingless bees; M. beecheii basis of native Mayan beekeeping in Yucatan
Wasps
Sphecidae
Microstigmus comes, the only known eusocial wasp that is not a member of the Vespidae
Vespidae, family of wasps with eusocial and non-eusocial subfamilies
Stenogastrinae (hover wasps), eusocial wasps from south east Asia
Eumeninae (potter wasps), common subsocial wasps that are the sister group to the eusocial vespids
Polistinae
Polistes, Mischocyttarus (paper wasps)
Epiponini, diverse group of tropical American wasps with medium/large perennial colonies, nests swarm-founded
Polybia, common genus of epiponines
Vespinae, annual nests enclosed in an envelope, founded by a single female wasp
Vespa (hornets), medium colonies, nests in buildings, tree cavities
Dolichovespula (wasps, yellowjackets), small colonies, aerial nests, sometimes in cavities
Vespula (wasps, yellowjackets), medium//large colonies, nests in soil, buildings, tree cavities
Vespula vulgaris (common wasp), most common British species; nest usually in lofts or in ground
Formicidae (ants)
Ponerinae, subfamily with mostly small colonies of large ants; primitive morphology
Dinoponera quadriceps (Dinosaur ant); world’s largest ant; queenless ant, small colonies
Formicinae, subfamily with many well-known species, almost half the British ant species are formicines
Oecophylla (weaver ants), very large colonies
Formica (wood ants), large/very large colonies
Myrmicinae, subfamily with many well-known species, almost half the British ant species are myrmicines
Monomorium pharaonis (Pharaoh’s ant), large colonies
Attini (fungus-growing ants)
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C1139 Social Insects. Diversity & Systematics. Lecture 5
Atta, Acromyrmex (leafcutter ants), Atta can have very large colonies
Dorylinae (African army ants) Dorylus (driver ants), very large colonies
Ecitoninae (American army ants), Eciton (army ants), very large colonies
Note: small colony means < 100, medium <1000, large >1000, very large >100,000
British social insect diversity
The table below has been compiled by F. Ratnieks from various sources. It is not necessary to learn this list. Use it as a
reference and to get an overall picture of the diversity of British eusocial Hymenoptera. Britain has a meager fauna,
especially for Polistinae wasps (1 European species that may be establishing) and termites (zero species). Britain has
reasonable diversity in bumble bees and Vespinae wasps, and the honey bee Apis mellifera is native. Even though we
have over 40 ant species this is small relative to total ant biodiversity. Britain also has some gall aphids with soldiers.
Termites, Isoptera
0 species
Ants, Formicidae
43 species
Ponerinae*
2
Ponera
Hypoponera
Myrnicinae*
19
Strongylognathus
Solenopsis
Myrmecina
Tetramorium
Stenamma
Formicoxenus
Leptothorax
Myrmica
Monomorium
Dolichoderinae
2
Tapinoma
Formicinae
20
Formica
Lasius
Wasps
1
1
(introduced, in greenhouses)
1
1
1
1
2
1
4
8
1
(live in hollow twigs in leaf litter, small cavities)
(including the "red ant")
(introduced, Pharaoh’s ant M. pharaonis, an indoor pest)
2
11
9
(wood ants)
(including the "pavement ant" L. niger)
10 eusocial species
0
Sphecidae
Vespidae
10
Polistinae
Polistes
1
Vespinae
9
Vespa
Dolichovespula
D. norwegica
D. sylvestris
D. saxonica
D. media
Vespula
V. austriaca
V. rufa
V vulgaris
V. germanica
Bees
1
paper wasps; the European species Polistes dominulus
has recently been found in the south and may establish
1
4
the hornet, Vespa crabro, very large wasps
("wasps"—nests usually exposed, look like rugby balls)
Norway wasp, common in Sheffield area, northern
tree wasp, common in Sheffield area, southern
Saxon wasp, recent arrival from Europe
Euro wasp, recent arrival from Europe, large wasps
("wasps"—nests usually in the ground or in a cavity)
workerless social parasite of V. rufa
small colonies with nests built at ground level
the common wasp, and Sheffield's commonest species
the German wasp, like V. vulgaris but more southern
4
Halictidae
40 eusocial species
13
Apidae
26
Meliponinae
Bombinae
Bombus
Apinae
none of the British species is eusocial
13 eusocial species, probably more
0
25
19
6
bumble bees
workerless social parasites, Bombus (Psithyrus)
1
Apis
1
the honey bee or western hive bee, A. mellifera
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C1139 Social Insects. Diversity & Systematics. Lecture 5
Anthophoridae
0
none of the British species is eusocial
8