Large, predatory water bugs – Alisha Steward

Many families in the Order (‘bugs’), Suborder (‘true bugs’), are aquatic, living in rivers, streams, ponds, lakes and other wetlands – and almost all aquatic bugs are predatory. This issue's creature feature focuses on two related families of aquatic Hemiptera – Belostomatidae and (Fig. 1). Belostomatids are known as giant water bugs. Some nepids are known as water , as they have a broad, leaf-like body, and others are known as needle bugs, as they have a thin, stick-like body.

Fig. 1. Water bug body forms and their faces that only a mother could love: a) Giant water bug - insulanus (Belostomatidae), b) Diplonychus sp. (Belostomatidae), c) and d) water - sp. (Nepidae), e) needle bug - dispar (Nepidae), and f) needle bug (Nepidae). Photograph a) by Peter Chew (www.brisbaneinsects.com) and photograph e) by the Murray-Darling Freshwater Research Centre (www.mdfrc.org.au/bugguide/index.htm) are used with permission Species of both belostomatids and nepids are large (15-75 mm long), and quite scary bugs at that, as they can inflict a nasty bite! They are differentiated from other aquatic bugs by their large size, the presence of raptorial forelegs (except in one African ), and the presence of paired respiratory processes at the tip of the abdomen (Andersen and Weir, 2004). In belostomatids the respiratory processes form short, retractable ‘air straps’, and in nepids they typically form a long siphon.

Belostomatids and nepids spend most, if not all of their life in water, although both groups have winged adult stages capable of flying between water bodies and are quick to colonise new habitats (Gooderham and Tsyrlin, 2002). They can be attracted to lights at night, and some nepids can even end up in swimming pools! I have observed nepids in chlorinated swimming pools, presumably breathing through their respiratory siphon at the end of their abdomen - poked through the surface film and used much like a snorkel. They don’t seem too fussy about water quality – on the Australian SIGNAL (Stream Grade Number Average Level) scale used to rate the tolerance or sensitivity of water bugs to pollution, belostomatids score 1 out of 10, meaning that they are extremely tolerant of pollution, and nepids score 3 out of 10, suggesting that they are moderately tolerant of pollution (Chessman, 2003).

Habitat and diet Belostomatids and nepids occur throughout Australia. They prefer still or slow-moving water, and are usually found at the edge of streams or ponds where aquatic

Fig. 2. Typical predatory water bug habitat in south-east Queensland – a shallow dam containing leaf litter. plants are present. Both types of bugs are brownish in colour and are well camouflaged amongst mud, leaves and twigs. They are typically ambush predators that sit and wait for prey. Prey includes other , tadpoles, small frogs and even , all of which are captured with their forelegs. As a result of their dietary preferences, belostomatids have been found to be a nuisance in fish farms (Carver et al., 1991).

In preparation for this article and its accompanying cover drawing by Lois Hughes, I visited Lois’ property at Mt Cotton to look for our artist’s models. The creek yielded many water bugs, but no belostomatids or nepids. Next, we visited a dam on the property, which was shallow and had a great deal of leaf litter on the bottom and around the edges (Fig. 2). A few scoops of the dip net revealed almost a dozen water scorpions! See Fig. 3 for a photograph of some that we collected. Predatory water bugs are often the last aquatic invertebrates to be seen in drying waters, so it was no surprise to see them in this shallow dam. They prey on any remaining aquatic invertebrates, and then fly off when the water dries up. Lois kept a few of the water scorpions for observation, and in order to feed them offered them a grasshopper. The grasshopper was quickly grasped and greedily devoured.

Life cycle Males in both families can Fig. 3. Spot the water bugs! There are two water scorpions produce sound to attract females for mating, and (Nepidae: Laccotrephes sp.) in this photograph. Note their often initiate mating by leaf-like appearance. ‘display-pumping’ or rhythmical push-up-like body movements near the water’s surface. Female belostomatids from the genus Diplonychus lay their eggs on the back of the male for protection (Fig. 4), whereas females of the genus Lethocerus lay eggs above the water on emergent vegetation that are defended by males in the water below the egg mass (Andersen and Weir, 2004). Nepid eggs possess respiratory horns, and are deposited at the water's edge or within plant tissue in a way that the horns are exposed to the air for respiration. Eggs of both families hatch into nymphs, which are similar to the adults – only smaller and usually lacking wings. Nymphs reach the adult stage in 5 moults (Gooderham and Tsyrlin, 2002).

Interesting facts! I observed one of the water scorpions ‘playing dead’ after it was touched – it rolled over, drew its legs against its body, and stopped moving (Fig. 5). I imagine that this response is to confuse and hide from potential predators, as once they stop moving they blend Fig. 4. Male Diplonychus sp. (Belostomatidae) with eggs. in well with leaf litter and other debris.

Giant water bugs are consumed throughout many Asian countries. There are many photographs of these bugs prepared as food – usually fried – on the web. Here is a link to an example (there are many more if you search): http://www.flickr.com/photos/cibergaita/56687803/

Conclusion Andersen and Weir (2004) state that the biology of many Australian species is poorly known. This is in stark contrast to our knowledge of many Fig. 5. This water scorpion (Nepidae: Laccotrephes sp.) appeared to ‘play dead’ when touched. other invertebrate groups, particularly butterflies, where we know much more about the biology of individual species (and even sub-species) – such as what plants they lay their eggs on, what time of year they are on the wing, how long the pupal stage lasts, and even information about caterpillar parasitoids. The lack of species-specific information is the reason that this article features a group of taxa, rather than one species. Aquatic Hemiptera, particularly belostomatids and nepids, are common in Australia, can be found in farm dams and backyard ponds, and can be reared in captivity, making them easy to study. These interesting water bugs are certainly worthy of more detailed research.

Classification and species checklist Belostomatids and nepids belong to the superfamily Nepoidea. The family Belostomatidae is recognised in Australia by only 2 genera: Diplonychus and Lethocerus. The family Nepidae is represented in Australia by 5 genera – Austronepa, Cercotmetus, Goondnomdanepa, Laccotrephes and Ranatra. Austronepa and Goondnomdanepa are endemic to Australia.

Australian species checklist (based on Hawking et al., 2009):

Order Hemiptera Suborder Heteroptera Infraorder Superfamily Nepoidea

Family Belostomatidae – giant water bugs Diplonychus eques Dufour Fabricius Lethocerus distinctifemur Menke Lethocerus insulanus Montandon

Family Nepidae Subfamily Nepinae – water scorpions Laccotrephes tristis Stal Subfamily Ranatrinae – needle bugs Austronepa angusta Hale (endemic) Cercotmetus brevipes Lansbury Goondnomdanepa brittoni Lansbury (endemic) Goondnomdanepa prominens Lansbury (endemic) Goondnomdanepa weiri Lansbury (endemic) Ranatra dispar Montandon Ranatra diminuta Montandon Ranatra ocidentalis Lansbury

References Andersen, N.M. & Weir, T.A. (2004). Australian Water Bugs: Their Biology and Identification (Hemiptera-Heteroptera, & Nepomorpha). Apollo Books, CSIRO Publishing: Collingwood, Victoria. Carver, M., Gross, G.F. & Woodward, T.E. (1991). Hemiptera. In: ‘The of Australia: A Textbook for Students and Research Workers.’ Chapter 30, 2nd Edition, Volume 1. Melbourne University Press. Pp. 429-509. Chessman, B.C. (2003). New sensitivity grades for Australian river macroinvertebrates. Marine and Freshwater Research, Volume 54: 95-103. Gooderham, J. & Tsyrlin, E. (2002). The Waterbug Book: A Guide to the Freshwater Macroinvertebrates of Temperate Australia. CSIRO Publishing: Collingwood, Victoria. Hawking, J.H., Smith, L.M., Le Busque, K. (editors) (2009). Identification and Ecology of Australian Freshwater Invertebrates. http://www.mdfrc.org.au/bugguide Version January 2009. Accessed 20/01/2013.

This article appeared in Issue Number 68 of “Metamorphosis Australia” in March 2013

Further reading Online identification key to distinguish between the families Belostomatidae and Nepidae (the same website can be used to identify other aquatic invertebrates) – http://www.mdfrc.org.au/bugguide/display.asp?type=4&class=17&Subclass=&Order=3&Family=&genus=&sp ecies=&couplet=14&fromcouplet=13 Peter Chew’s website to insects and spiders of Brisbane, including aquatic invertebrates: www.brisbaneinsects.com

Solution to Fig. 3:

Photos, except where otherwise credited, Alisha Steward