Who Said Cockroaches Are Not Colourful!

On a recent trip with some James Cook University students, a few remarked that they had no idea tht cockroaches could be so colourful.

Well here are a few examples that will hopefully challenge your perception of these insects as being rather dull creatures that often invade human habitation. The fact is that most species have little to do with humanity and could not survive long in our homes, restaurants, hotels etc. We just don't
"offer" what they are looking for!

This one, the Inland Ellipsidion, Ellipsidion amplum Hebard literally flew into me while I was walking on a Cairns street in the centre of town. It is a diurnal species that lives on flowers where it feeds on pollen and nectar. The bright orange colour pattern suggests Mullerian Mimicry.

The Inland Ellipsidion Ellipsidion amplum Hebard, dorsal and ventral views.

Ellipsidon cockroaches are fairly common across the continent where they have a rather similar appearance. This is among the largest of species measuring 17 mm.

The above-noted specimen was a bit battered after being carried around in a shopping bag for a few hours. Here is an example of the species in much better condition. Note the orange-tipped antennae. Other species have the antennae with white tips. In addition, the antennae are very hairy (click on the photo to enlarge), a condition quite unusual in most Australian cockroaches.

Ellipsidion is a member of the large family Ectobiidae (formerly Blattellidae) and is in the subfamily Pseudophyllodromiinae. This is quite a mouthful. However, species in this subfamily are usually very attractive. Here are a few examples.

 The Australian Allacta, Allacta australiensis Roth. 

This species lives in rainforests where it can be found only on tree trunks. It seems to prefer certain trees and not others. It measures 11 mm and is active at night.

 The Variable False Pseudobalta, Pseudobalta cinctella (Hebard)

Pseudobaltas are tropical cockroaches that are active at night. They have been found under bark during the day. The species has a broad distribution across the continent and the markings on the thorax (pronotum) are variable. It is small, measuring about 6 mm in length.

 The genus Balta includes some 39 described species in Australia. There are many undescribed species, like the one above. Baltas are distinguished on the basis of colour and morphological structures. They are nocturnal and live in leaf litter during the day. Their numbers are often great and they probably serve as food for many other organisms. All known species are active after dark.

 The Pretty Balta, Balta verticalis Hebard.

This Balta is aptly named. The specific name refers to the stripes between the eyes. It is a fairly common tropical species in northeast Australia where it can be found in rainforests and along rainforest margins. It measures about 12 mm in length.

 The Grey Balta, Balta scripta (Shelford)

One of the commonest Baltas in the northern Tropics, this species spends the day in leaf litter and is active at night. It frequently comes to lights. The pattern on the pronotum and greyish colour is very characteristic. 

The Small Mediastinia, Mediastinia australica (Shelford)

Mediastinias are more common than previously thought. They are very small, measuring less than 5mm in total body length. They are very colourful and have a very flattened appearance. This facilitates diurnal life in leaf axils and unfurling leaves. After dark they emerge to feed on particulate matter found on leaf surfaces.

The variable Speedy Cockroach, Choristima bimaculata Roth

This cockroach is another nocturnal species but it  belongs to another ectobiid subfamily, the Ectobiinae. Seldom seen during the day, adults can be attracted to light late in the evening. This species has a number of different morphs based on the pattern of the pronotum and wings. They are small, measuring less than 5 mm in total length.

Sloane's Northern Wingless Cockroach, Cosmozosteria sloanei Shaw.

This is an example of the most characteristic group of Australian Cockroaches, the subfamily Polyzosteriinae of the Blattidae. Everyone who has wandered around in the outback or the mixed woodlands of the tropics has come across these large cockroaches abroad during the day. They are very conspicuous in their colour patterns and they seem to be walking bags of nasty chemicals. They are avoided by birds and lizards. This one is about the size of a 20 cent Australian coin.

But these insects are the topic of a future blog.