Blattodea contains over 4500 species worldwide, with about 150 species in Europe. They are among the most ancient winged insects, the earliest fossils dating back to the Carboniferous. The group is well defined by a combination of characters: eggs usually contained in oothecae (egg cases), leathery forewings, male genitalia asymmetrical and cerci* with one or more segments. Most cockroaches are tropical and found in a wide variety of habitats such as dead or decaying leaves or trees, caves, under stones, in nests of social insects etc. Cockroaches are mostly scavengers eating organic material. Less than 1% (30 species) are associated with humans, but these species contribute to the unpopular reputation of these insects. Cockroaches exhibit diverse reproductive biology. Most species have sexual reproduction, but some populations of Pycnoscelus surinamensis are parthenogenetic. These hemimetabolous insects produce hardened oothecae deposited on a substrate or membraneous oothecae that are incubated in a brood sac within the female’s body. Some species exhibit a high level of parental care.
*Cercus (sg.), Cerci (pl.): paired sensory structures at the posterior end of some arthropods.
Cockroaches are mostly nocturnal insect, with biting mouthparts and legs that are adapted for swift running. The body is oval and dorsoventrally flattened, allowing the animals to hide in narrow spaces, for example under bark or in crevices of trees and rocks. The head is usually hidden beneath the pronotal shield, and there is a pair of short cerci at the end of the abdomen. In winged species, the forewings (tegmina) are leathery and protect the delicate hindwings.
Most cockroaches are scavengers, with fairly broad diets, but a few species in the family Cryptocercidae specialize on dead and decaying wood. Some cockroaches invade human dwellings and are significant household pests.
Upper Carboniferous to Recent. One of the dominant groups of the late Palaeozoic.
Order Blattodea is also known as Order Blattaria. The species are commonly known as cockroaches. They usually range from two millimeters to over sixty millimeters in length, but some cockroaches have been measured at about 100 millimeters. Most species have two pairs of wings, but wingless species are known. They are quick and use this trait as a tactic to scurry away from predators. Sexual dimorphism can be seen in some species. They live in caves, forest canopies, and under bark. Almost all of the species are nocturnal. Cockroaches undergo incomplete metamorphosis. Pheromones are used to attract potential mates. The females usually produce an egg case called oothecae. Cockroaches can live for five to over forty days without water and food. If water is available they can survive for about 60 to 90 days without food. Though they can survive without resources for days, they have many natural enemies. Spiders, frogs, toads, centipedes, wasps, lizards, birds, geckos, mantids, ants, beetles, and mice feed on cockroaches. They can be seen in the fossil record as far back as the Upper Carboniferous.
- eggs usually contained in ootheca
- leathery forewings.
- male genitalia asymmetrical
- cerci variable, with one or more segments
There are over 4,000 species of roaches spread all around the globe, and lots more still unknown to science. In Michigan there are only a couple of dozen species, and about half of them are invaders that came along with European settlers.
Biogeographic Regions: nearctic (Native ); palearctic (Native ); oriental (Native ); ethiopian (Native ); neotropical (Native ); australian (Native )
Cockroaches are long, flat, brown insects. Their heads point downward and have chewing mouthparts. A plate from the top of the thorax covers the head when you look down on them, so you can't actually see the head. They are very fast runners. They have long antennae, and at the end of the abdomen are two short antennae-like structures that sense air current and vibrations.
Other Physical Features: ectothermic ; bilateral symmetry
Sexual Dimorphism: female larger
Most cockroach species live in dead leaves and soil on the ground in forests. A few well-known species have adjusted to living with people in houses and other buildings.
Habitat Regions: temperate ; tropical ; terrestrial
Terrestrial Biomes: taiga ; desert or dune ; chaparral ; forest ; rainforest ; scrub forest ; mountains
Roaches are scavenging omnivores, they'll eat just about any organic matter they can find. They don't have a powerful bite, so they don't usually eat living animals.
In wild habitats, roaches help breakdown dead plants and animal waste.
Ecosystem Impact: biodegradation
Most roach species don't have any special defenses, they just hide, only come out in the dark, and run fast. A few species have chemical defenses.
- small Squamata
Known prey organisms
Based on studies in:
Costa Rica (Carrion substrate)
This list may not be complete but is based on published studies.
Life History and Behavior
Communication and Perception
Most roach species use touch and taste/smell as primary senses, but some also communicate with vibrations or other sounds. They hiss, or rub their wings together. The sound startles predators and gives roach a chance to escape, and is sometimes used to attract the opposite sex.
Cockroaches have incomplete metamorphosis. Immature roaches look pretty much like adult roaches, except they don't have wings yet. As they grow the molt (shed their whole skin at once) several times. After the last molt, they roach has wings and can reproduce. It stops growing and molting at that point.
Lifespans vary with species. Some can live for two years.
Female roaches produce dozens of offspring several times in their lives. Most species produce an egg case with up 40 eggs. A few species keep the eggs in their abdomen until they hatch, and some actually give birth to live young.
Breeding season: Wild roaches breed in the summer, but in urban habitats they can breed any time.
Key Reproductive Features: iteroparous ; seasonal breeding ; year-round breeding ; sexual ; fertilization (Internal ); viviparous ; ovoviviparous ; oviparous
Most roach species, including the ones that live in houses, don't have any parental care. In some of the woodland species females guard over their young for a short time after they hatch. A few species live together in burrows in dead wood.
Parental Investment: no parental involvement; female parental care
Evolution and Systematics
Systematics or Phylogenetics
Mantodea, Isoptera, and Blattaria are usually combined by entomologists into a higher group called Dictyoptera. Current evidence strongly suggests termites evolved directly from true cockroaches, and some authors now consider termites to be an epifamily of cockroaches (Eggleton et al. 2005), as the Blattaria excluding Isoptera are not a monophyletic group (Grimaldi & Engel 2005).
No roach species are considered endangered.
Relevance to Humans and Ecosystems
Economic Importance for Humans: Negative
Cockroaches are the biggest household pest problem in most cities and towns. They spread bacteria that can make people sick.
Negative Impacts: injures humans (carries human disease); household pest
Economic Importance for Humans: Positive
The great majority of roach species never bother people. They live outside, and are a harmless part of foodwebs.
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