The Hymenoptera is the third largest order of insects, with over 150,000 living species, including sawflies, ants, bees, and wasps. The order derives its name from the Greek word ‘hymen’ as the members of this group have membranous, connected wings.
These insects are abundant in almost all habitats, particularly in tropical and subtropical regions. They are a widely beneficial group that participates in flower pollination and prepares honey. While some are parasitic, living inside their hosts, other nonparasitic species are carnivorous, phytophagous, or omnivorous.
The order is further divided into two suborders: the Symphyta (with no waist) and Apocrita, which have narrow waists.
They are a group of small to medium-sized insects. The smallest hymenopterans, the fairyflies, measure about 0.21 mm (about 0.008 inches) in length, whereas the largest, belonging to the family Pelecinidae, may exceed 5 cm (about 2 inches) in length.
The body of hymenopterans is divided into three main segments: head, thorax, and abdomen. The thoracic region has two pairs of membranous wings and a narrow waist, which sets it apart from the abdomen.
The mouthparts comprising the maxillae and mandibles are modified appendages found in the head region. In many species, these mouthparts are modified into lengthy proboscis to suck nectar from flowers. The sensory antennae on the head are usually moderately long, with multiple segments. They also have large compound eyes and three simple eyes, or ocelli, arranged in a triangle on top of the head.
The hind wings possess multiple hooked bristles or hamuli on their anterior margin, which enables both the forelimbs and the hindlimbs to stay interlocked. While smaller species have two to three hamuli, larger ones have more.
Females have an egg-depositing organ called the ovipositor at the tip of their abdomen. In sawflies, it is saw-like, modified for making slits in plant parts, whereas in all other hymenopterans it is adapted for piercing. In bees and wasps, the ovipositor forms a stinger at the tip for injecting venom into predators and prey.
In the larval stage, hymenopterans have a distinct head region, three thoracic segments, and nine to ten abdominal segments.
Symphyta
The larvae of this order are eruciform, resembling caterpillars in appearance. They have large mandibles, ocelli, three pairs of thoracic limbs, and, usually, six or eight abdominal prolegs (small yet-to-develop stubs of legs). Unlike those in the order Lepidoptera, these prolegs lack crochet hooks at their tips.
Apocrita
These larvae are maggot-like with no legs or ocelli. Their hindgut remains closed during development, while the anus opens only after completion of growth. The larvae have ten pairs of spiracles or breathing pores in bees, ants, and stinging wasps.
Parasitic Forms
In the larvae of parasitic hymenopterans, the head is often reduced and partially withdrawn into the anterior portion of the thorax. The antennae are either absent or greatly reduced in size, while the mandibles are tooth-like, sickle-like, or spine-like. They usually have nine pairs of spiracles.
Hymenopterans are divided into two suborders: Symphyta and Apocrita. Members of Symphyta, the sawflies, have no constriction between the thorax and the abdomen, whereas the bees, ants, and wasps comprising Apocrita are characterized by a constriction between the first and second abdominal segments (petiole).
The suborder Symphyta is sometimes considered paraphyletic because the Orussidae family, a group of sawflies, is believed to be the ancestors of Apocrita.
While bees and wasps are found in virtually any region where flowering plants exist, ants are abundant, mainly in the tropics and subtropics. However, Hymenopterans are almost absent in regions north of the Arctic Circle.
Most hymenopterans are phytophagous, feeding on plant matter, such as flowers, stems, pollen, or nectar. Bees consume pollen and nectar from various flowering plants, including milkweed, dandelions, clover, goldenrod, and fruit trees. While ants prefer honeydew, seeds, and nectar, they often feed on small insects.
Many wasps are parasitoid and feed on the host’s body fats and fluids. Some hymenopterans are intermediates between herbivorous and parasitoid forms and live off food stolen from galls or nests of other insects.
Both sexual and asexual reproduction is found in Hymenopterans.
Among hymenopterans, females are produced by eggs fertilized by sperm, whereas unfertilized eggs produce males. This phenomenon is called haplodiploidy since females are diploids with two sets of chromosomes from the contributing male and female, whereas the male is haploid, with only a single set of chromosomes obtained from the female. The egg-laying female has complete control during fertilization and thus determines the sex of her offspring.
Asexual reproduction through parthenogenesis occurs in some hymenopterans, where the embryos are formed without fertilization. The desert ant (Cataglyphis cursor), the clonal raider ant (Cerapachys biroi), and the predaceous ant (Platythyrea punctata) undergo a special kind of parthenogenesis called thelytoky, where only female diploid embryos are produced through automixis (fusion of haploid gametes from the same individual).
Welcome to AnimalFact - your go-to source for fascinating insights into the amazing world of animals!
