Welcome to my blog

This is where I post various musings about wildlife and ecology, observations of interesting species (often invertebrates)
and bits of research that grab my attention. As well as blogging, I undertake professional ecological & wildlife surveys
covering invertebrates, plants, birds, reptiles, amphibians and some mammals, plus habitat assessment and management
. I don't work on planning applications/for developers. The pages on the right will tell you more about my work,
main interests and key projects, and you can follow my academic work here.

Tuesday 24 January 2012

Observations of Macleay's Spectres II: the boys

Having looked at the early stages (eggs and small nymphs) of my Macleay's Spectre stick insects (Extatosoma tiaratum), it's time to move on to looking at the older males. As they develop through a series of nymphal stages (instars), moulting and expanding in order to grow, they develop small spines and flanges, but most obviously a pair of wing buds. In their final (5th) instar, these are quite obvious and when they moult, emerging as an adult, these develop into full pleated wings with long 'coat-tail' covers. 

An adult male showing its long wing covers.
An adult male opening its wings just as it is about to take flight.
Once they have dried their wings (much like butterflies and other winged insects do), the males are able to fly strongly, and in the wild do so in order to find food and females, or to evade predation. However, I found that initially they were not very active apart from showing increased aggression when handled. During their final moult they also develop longer, curved antennae and larger, more protruding eyes, presumably used to find females both by scent at a distance and then visually when nearer. The wings fold along radial pleats (a bit like a parasol) and have a spotty pattern, and the neck is long and flexible at the joint with the thorax.

Head-on shot of a male in a threat posture showing well developed eyes and antennae.
The males remain well camouflaged, moving in a similar manner to leaves in the wind. For a few weeks they retained their variable colouring - some males were greenish, others brown or greyish. However, after this time a change seemed to take place with most darkening to a reddish-brown colour, and becoming more willing to fly - most evenings, the vivaria are opened and some males readily walk onto my outstreched hand and then launch (this is preceded by a subtle but definitie raising of the body into a launch posture), often having climbed onto my head or shoulder first. Around the same time, the first males could be found mating with the large adult females (more about them in Part III). So, it appears - albeit anecdotally - that this change in colour signals sexual maturity. If so, this is interesting as it does not seem to be associated with increased aggression either towards me (if anything they seem less aggressive when handled and simply fly more readily, though they may simply have habituated to handling, and some definitely avoid handling if possible) or other males. A number of males can be seen clustered around a female on occasions, but I have witnessed to overt aggression, though I have to assume that there is some form of competition to mate - maybe I need to observe what they are doing at 3am...

A male showing a dark red-brown colour and the long neck. The bright dot on top of the head is one of the male's ocelli (simple eyes).
A yellow-brown late (5th?) instar male nymph with the long wing-buds just visible behind the right middle leg.
Another late-instar (again, 5th?) male nymph, this one pale green in colour, again with the wing-buds visible.
When mating (or preparing to do so), males lie lengthwise along the back of a female (in the usual legs-outstretched 'stick' position) and both have genitalia at the rear of the flexible abdomens which bend to fit. The function of the long male neck with flexible articulation then becomes evident; females often arch backwards when feeding or moving and this forces the male's head backwards - the flexible neck allows him to remain in position without damage.

Males using my wife as a climbing-frame/launchpad while their cage is being cleaned. Just prior to this photo being taken, one of the males appeared to be trying to mate with her hair-grip (it has strong legs and a handy, accommodating central groove...)

Sperm transfer takes place in the form of a spermatophore - a packet of sperm in a hard 'shell' which novice insect keepers sometimes mistake for eggs. The spermatophore of E. tiaratum was noted by Clark (1975) and has been well documented since, but it was not until relatively recently that review of research and observations (e.g. Bragg, 1991) concluded that this structure provided the usual method of sperm transfer in the order Phasmida (AKA Phasmatodea). I recently collected an E. tiaratum spermatophore from the floor of one of my containers at home. The photo below shows the outer structure - the thread attaches it to the male during transfer to the female and the sperm-containing sac is 2.5-3mm in diameter, the whole being white with a pink tinge especially where the thread attaches to the sac.

Spermatophore of E. tiaratum
That's all for the males, but why not check out Part III: the girls...


Bragg, P.E. (1991). Spermatophores in Phasmida. Entomologist 110(2): 76‑80.
Clark, J.T. (1975). A conspicuous spermatophore in the phasmid Extatosoma tiaratum Macleay. Entomologist's Monthly Magazine 110: 81-82

No comments:

Post a Comment