Blattodea

Blattodea is an order of insects that contains cockroaches and termites. Collectively, Blattodea and the mantis order Mantodea are considered part of the superorder Dictyoptera. Formerly, termites were considered the separate order Isoptera, but genetic and molecular evidence suggests they evolved from within the cockroach lineage, which renders them cockroaches cladistically; the group of termites were subsumed into Blattodea and they are considered by some to be a divergent group of cockroaches. Blattodea includes approximately 4,400 species of cockroach in almost 500 genera, and about 3,000 species in around 300 genera within the termite clade.

Termites are pale-coloured, soft-bodied eusocial insects that live in colonies with a biological caste system. A pair of sexually mature reproductives, the king and the queen, breed to produce all other individuals within the colony, consisting of the numerous and sterile (non-breeding) workers and soldiers. In contrast, cockroaches are pigmented (often brown) and possess sclerotised body parts hardened with sclerotin. Cockroaches are not colonial but do have a tendency to aggregate, with some species considered to be pre-social as all adults within a social group are capable of breeding. Termites and cockroaches share several similarities, including various social behaviours, trail following, kin recognition, and methods of communication.

Cladistic analysis of five DNA sequences in 107 species representing all the termite subfamilies, all six cockroach families, including 22 of the 29 subfamilies, and five of the 15 mantis families (as outgroups) showed that the termites are nested within the cockroaches, and that the monotypic Cryptocercidae is a sister group to the termites, which is reinforced by Cryptocercus sharing characteristics such as particular gut bacteria species with termites. The mantids were shown to be the sister group to Blattodea.

The cockroach families Lamproblattidae and Tryonicidae are not shown but are placed within the superfamily Blattoidea. The cockroach families Corydiidae and Ectobiidae were previously known as the Polyphagidae and Blattellidae.

The evolutionary relationships of the Blattodea (cockroaches and termites), based on Eggleton, Beccaloni & Inward (2007) and modified by Evangelista et al. 2019, are shown in the following cladogram, which depicts the family Alienopteridae (originally assigned to its own order "Alienoptera") as sister to Mantodea; while it was reassigned to the extinct Blattodea superfamily Umenocoleoidea by Vršanský et al., a more recent analysis places Alienopteridae and Umenocoleidae as sister taxa within Dictyoptera, and not within Blattodea.

Over 4,000 species of cockroaches are found in every corner of the globe with each continent having its own indigenous species. Most of these are omnivores or detritivores and live in a range of habitats such as among leaf litter, in rotting wood, in thick vegetation, in crevices, in cavities beneath bark, under logs and among debris. Some are arboreal, some live in caves and some are aquatic. A small number of species have taken to living in close proximity to humans in buildings, have been transported around the world by them, and are regarded as pests. Although some species harbour symbionts in their guts which facilitate cellulose digestion, many species also produce enzymes to digest cellulose independent of the symbionts.

Over 3,000 species of termite are found in all the continents except Antarctica. The greatest diversity is found in Africa and relatively few species inhabit Europe and North America. They are also detrivores and many species eat wood, having specialised guts with symbiotic protozoa to digest the cellulose. Termites have soft bodies and keep out of sight as far as possible. They can loosely be subdivided into dampwood, drywood and subterranean types. In general, dampwood termites inhabit coniferous forests, drywood termites inhabit hardwood forests and subterranean termites live in a wide variety of habitats.

Termites are eusocial insects that live in colonies. They have a caste system, with a king and queen in each colony and many non-reproductive workers. The workers forage for food which they bring back to the colony to feed the reproductives and the developing young. Cockroaches are also social insects but do not live in colonies, and all adults are able to reproduce. Some species form aggregations, others show an inclination to aggregate, and some exhibit parental care of their offspring.