Observations of Macleay's Spectres III: the girls

Following sections covering eggs and early nymphal stages and mature males, the third part of this series on Extatosoma tiaratum, the Macleay's Spectre, looks at mature females.

Female E. tiaratum with front legs raised.

As late-instar nymphs and adults, females are structurally very different from males (sexual dimorphism). They are larger - up to 150mm long with males around 100mm, broader and much heavier - up to around 30g (a lot for an insect and females often drag the spiny underside of their abdomen along the surface they are walking on, sometimes producing a clear scraping noise as they move). Females also have many more spines and flanges, including a more pronounced 'head-dress' of short blunt spines. In fact, in E. tiaratum, the differences between males and females are so pronounced that they were originally described as separate species (Hadlington & Johnston, 1998)! Details of female genitalia are given by Heather (1965) and note that from a sample of seven specimens there were on average 151 ovarioles (tubes forming the paired ovaries) with an average of seven oocytes (immature egg cells) each. The bursa copulatrix (the sac-like organ where the spermatophore or 'sperm packet' is stored after copulation) bears around 20 blind tubules and there appears to be no distinct spermatheca (sac for sperm storage) or other sclerotised (hardened) part of the genitalia. This matches the observation (see Part II) that sperm transfer is by spermatophore.

Flanges and spines on the leg of a female.

The spine-covered abdomen of a large female.

Side view of a female's head showing the oval extension of the top with its 'head-dress' of short spines. Also note that the camouflage includes marking breaking up the shape of the eye.

The head of a large female showing small wart-like bumps as well as a clear view of the mouthparts.

Around the same time my males changed to a brick-red colour, my two large females developed a pinkish-lilac tinge as shown in the photo of the abdomen above. This may be an indication of sexual maturity or possibly gravidity (containing eggs). Also, following their final moult, the adult females became noticeably more aggressive, making for interesting cage-cleaning sessions... This aggression included general attempts at evading capture (fleeing or dropping out of reach; previously these had not occurred often) plus active attempts to use spines as weaponry (such as pinching with the inner edge of a bent leg, nut-cracker style), including against unwary males that strayed too close soon after an angry female was replaced in the cage. I have seen one male with what appears to be a small healing puncture wound (i.e. a hardened drop of what I imagine to be dark haemolymph) on the ventral side of the thorax though whether this was caused by female aggression or an accident with a bramble thorn I do not know.

A female nymph already showing spines and flanges.

Side view of a late-instar female nymph.

As this pair of photos shows, the female structure develops at a relatively early stage, essentially just getting larger with each moult. This contrasts to some extent with males which show a number of significant structural changes following their final moult.

A big girl perching on my wrist. She is mighty!

So, I started this series of posts with eggs, and can return to this topic as two days ago one of the large females began laying eggs. This is not a precise process in E. tiaratum as eggs are flicked up to a few feet (maybe a metre or so) by twictching the abdomen when the egg is laid (this also occurs with frass AKA insect faeces which takes the form of dry 3mm x 5mm oval pellets of plant material - in males, frass is long and thin, approx 1mm x 5mm). Fortunately as my insects are in cages, the eggs are easy to collect so I hope to have another generation relatively soon.

Tip of a mature female's abdomen showing an egg about to be laid. Note the dorsal spines on the abdomen - they are splayed outwards which may be an adaptation to accommodate a male during mating.

A female nymph doing her favourite thing - eating bramble leaves, nom nom nom.

It's busy during cage-cleaning time.

References

Hadlington, P & Johnston, J.A. (1998). An Introduction to Australian Insects (revised ed.). University of New South Wales, Sydney.
Heather, N.W. (1965). Studies on female genitalia of Queensland Phasmida. Australian Journal of Entomology 4(1): 33-38.