Wasp

Genetics

In wasps, as in other Hymenoptera, sexes are significantly genetically different. Females have a diploid (2n) number of chromosomes and come about from fertilized eggs. Males, in contrast, have a haploid (n) number of chromosomes and develop from an unfertilized egg. Wasps store sperm inside their body and control its release for each individual egg as it is laid; if a female wishes to produce a male egg, she simply lays the egg without fertilizing it. Therefore, under most conditions in most species, wasps have complete voluntary control over the sex of their offspring.

Anatomy and gender

Wasp ocelli (simple eyes) and dorsal part of the compound eyes; also showing fine, unbranched hairs

Anatomically, there is a great deal of variation between different species of wasp. Like all insects, wasps have a hard exoskeleton covering their three main body parts. These parts are known as the head, metasoma and mesosoma. Wasps also have a constricted region joining the first and second segments of the abdomen (the first segment is part of the mesosoma, the second is part of the metasoma) known as the petiole. Like all insects, wasps have three sets of two legs. In addition to their compound eyes, wasps also have several simple eyes known as ocelli. These are typically arranged in a triangular formation just forward of an area of the head known as the vertex.

It is possible to distinguish between certain wasp species genders based on the number of divisions on their antennae. Male Yellowjacket wasps for example have 13 divisions per antenna, while females have 12. Males can in some cases be differentiated from females by virtue of the fact that the upper region of the male's mesosoma (called the tergum) consists of an additional terga. The total number of terga is typically six. The difference between sterile female worker wasps and queens also varies between species but generally the queen is noticeably larger than both males and other females.

Wasps can be differentiated from bees as bees have a flattened hind basitarsus. Unlike bees, wasps generally lack plumose hairs. They vary in the number and size of hairs they have between species.

The type of nest produced by wasps can depend on the species and location. Many social wasps produce paper pulp nests on trees, in attics, holes in the ground or other such sheltered areas with access to the outdoors. By contrast solitary wasps are generally parasitic or predatory and only the latter build nests at all. Unlike honey bees, wasps have no wax producing glands. Many instead create a paper-like substance primarily from wood pulp. Wood fibers are gathered locally from weathered wood, softened by chewing and mixing with saliva. The pulp is then used to make combs with cells for brood rearing. More commonly, nests are simply burrows excavated in a substrate (usually the soil, but also plant stems), or, if constructed, they are constructed from mud.

Tiphiid wasp, a solitary wasp.

Paper pulp type wasp colony on maple tree, photographed near Maple Lake in Cook County, Illinois in October 2008.

Solitary wasps

The nesting habits of solitary wasps are more diverse than those of social wasps. Mud daubers and pollen wasps construct mud cells in sheltered places typically on the side of walls. Potter wasps similarly build vase-like nests from mud, often with multiple cells, attached to the twigs of trees or against walls. Most other predatory wasps burrow into soil or into plant stems, and a few do not build nests at all and prefer naturally occurring cavities, such as small holes in wood. A single egg is laid in each cell, which is sealed thereafter, so there is no interaction between the larvae and the adults, unlike in social wasps. In some species, male eggs are selectively placed on smaller prey, leading to males being generally smaller than females.

Generally wasps are parasites or parasitoids as larvae, and feed only on nectar as adults. Many wasps are predatory, using other insects (often paralyzed) as food for their larvae. A few social wasps are omnivorous, feeding on a variety of fallen fruit, nectar, and carrion. Some of these social wasps, such as yellowjackets, may scavenge for dead insects to provide for their young. In many social species the larvae provide sweet secretions that are fed to the adults.

Sand wasp (Bembix oculata, family Crabronidae) removing body fluids from a fly after having paralysed it with the sting.