Blattodea: Cockroaches

The Order Blattodea includes the cockroaches and Termites. There are >4,000 species world wide, with >450 species in Australia. Cockroaches have a bad reputation and the sight of one scurrying across the kitchen floor makes many people squeamish. This bad reputation is undeserved for the majority of cockroaches, we should not judge the entire order based on 4 or 5 pest species.

“Blatta” in Latin is used for insects that shun light.

The features that distinguish a cockroach from other insects are:

  • Hemimetabolous (incomplete metamorphosis – egg nymph, adult).
  • Bodies flattened on lower and upper surfaces (dorsoventrally).
  • Head hypognathous (jaws below head, mouthparts directed down – like in a grasshopper).
  • Mouthparts are designed for chewing.
  • Compound eyes vary in size from small to large, 2 simple eyes (ocelii).
  • Antennae are long and thin with lots of segments (filiform).
  • Behind the head is a shield like plate (pronotum) over the first segment of the thorax (prothorax) and that can cover the head in some species.
  • The thorax has two other segments, the mesothorax and metathorax, that are roughly rectangular and equal in size.
  • Forewings are hardened and leathery (called tegmen / tegmina).
  • Hindwings are membranous.
  • Legs have spines and the tarsi (bottom part of leg) has 5 segments on each leg. The top section of the leg (coxae) are large.
  • The abdomen has 10 segments that are visible.
  • The abdomen has cerci which can have multiple segments.
Cockroach with some parts labelled: Photograph by Sue Jaggar. Cockroach caught in South Perth

Cockroaches feed on pollen, bark and leaf material. The majority of species are nocturnal. Nymphs (juveniles) are smaller than adults, with different patterns. It is difficult to ID juveniles to species. Native cockroaches rarely enter homes. Female cockroaches carry around their egg sacks (called ootheca) until they are ready to hatch. They will often mate soon after the eggs hatch, although some species only mate once and can produce several egg sacs from this matin.

Native cockroaches in Kings Park. (a) Ellipsidion humerale adult. on Verticordia cooloomia (b) to (d) Ellipsidion australe juvenile on Verticordia plumosa and Banksia burdetti. Photographs by Sue Jaggar.

By Sue Jaggar