Archive for the 'Hymenoptera' Category

Green Tree Ants

June 5, 2010

What a crazy couple of weeks. Amazing amounts of work to catch up on, lots of reading and to cap it all a broken tooth (with a subsequent visit to the dentist). My trip seems like a distant memory!

Anyway.. I thought I would start off by putting up a few pics of my favourite ant. The green tree ant (also called a weaver ant) is very common in its favoured habitats, across the tropics of Australia. Why do I like them? Well, to my eyes they are quite graceful, with clean lines and a great colour. Usually they are yellow/orange with a greenish tinge forward of the petiole, and have a nice rich green gaster. They are also easy to find, and easy to photograph (i.e. large, slowish, and inquisitive aggresive). The scientific name, Oecophylla smaragdina, seems to have a different pronunciation for every entomologist I speak with. I use Ee-cof-illa sma-rah-dina. Any opinions?

Green tree ants have some really interesting behaviours too, which because of the aforementioned qualities, are easy to observe. They build their nests from living leaves, which they stitch together using silk produced by the larvae. It looks literally as they they are sewing; the worker holds a larva in her mandibles and moves it back and forth over a join, while other workers hold the leaves together using their freakily sticky feet and impressive weight-holding ability (see Archetype for some great info on sticky feet, here and here). A single colony can span multiple trees, with many of these nests in varying sizes. They are great communicators, and use vibrations in addition to chemicals. Tap on a nest a few times and not only do the occupants come running, but a few minutes later you will have ants from a fair distance around the tree racing towards you (wildly spraying acid!)

They are voracious predators, as can be seen in the photo below. Lacking a sting, they ‘spread eagle’ their victim, rendering it helpless against the rather brutal butchering which follows. This gruesome scene unfolded at our kitchen window each evening, where the ants feasted upon the various bugs attracted to the window. On more than one occasion they tried to pin down small geckos too!

Like many ants, they also tend hemiterids for the sweet solution they produce in return for protection from predators.Where available, they also visit extra-floral nectaries as in the photograph below. I was surprised at how much fluid these nectaries were producing, with a new droplet forming within seconds of being consumed. You can just see the nectar drop forming on the nectary (about 1/4 of its normal quantity), just below the elbow of the ant’s right antennae.

One last thing.. if you ever find a colony of these guys in a tree, check the ground where you’re going to stand first. I stood in a feeding column while watching a nest which was at head height. Didn’t realise until I started to get nasty nasty pin-prick pains up and down my lower legs! They have a mean pair of mandibles, and to cap it off, like to spray a bit of acid in the wound!

Holidays… don’t they go quick!

May 22, 2010

Back from a great holiday up in the Daintree. Saw lots of cool stuff, and had a great time catching up with my parents (who live overseas). I will get some pics up online this week, but I had better get stuck into the mountain of dirty laundry which is stinkin’ it up in the bags! Appears I also have a tonne of reading (blogs, emails, papers) to catch up on.

Found these little guys on the beach yesterday, tidying up the remains of a frog. Always tickles me to see an invertebrate coming out on top! I had no hand lens nor means of retaining a couple,  only my wife’s compact digital camera so am not too sure of the ID. Looks to be an Iridomyrmex sp….

Ant Plants

April 1, 2010

Mutualism in nature has always been something that interests me, and in my eyes one of the more amazing examples would have to be the relationship between certain ants and plants. These relationships can be relatively simple, where the plant produces supplemental food, or more complex with the plant providing a home for the ants.

Plants which produce supplementary food can do so via small food nodules, or by the production of sugary secretions at extrafloral nectaries (basically, a nectary outside of a flower). These attract ants, which benefit from the easily harvested nutrient, and in turn this benefits the plant because the ants defend the food supply.

The next step up is plants which actually create an area for the ants to inhabit (domatia). These can range from simple hollow thorns, such as in Acacia sphaerocephala, to the more complex tunnel networks found in the tuber of the Myrmecodia. Now here’s a superb example of a refined mutualistic relationship. This plant gains both a defense mechanism and a food source from its association with ants. Myrmecodia are epiphytes (they live on other plants), and are somewhat unusual in appearance, as the bulk of the organism is usually made up of the tuber (some call this the caudex, which is a modified stem). Within this tuber is a network of tunnels, some with smooth walls which the ants live in, and some covered in nodules in which the ants deposit their refuse. This refuse is then used as nutrient by the plant. A variety of ant species have been found living in these plants and in Australia they include Philidris cordatus (most common inhabitant), Pheidole megacephala and Crematogaster physothorax (Huxley, 1978). Even frogs have been found using them as a temporary home!

No prizes for photography... a young Myrmecodia beccarii found on the beach.

The fact that organisms from two completely separate kingdoms have managed to co-evolve and work so efficiently together is always pretty neat.

Huxley, Camilla R. 1978. The Ant-Plants Myrmecodia and Hydnophytum (Rubiaceae), and the Relationships between their Morphology, Ant Occupants, Physiology and Ecology. New Phytologist.

As a side note… how’s this for a title!

Amador-Vargas, S. 2008. Spartan defense in the Thermopylae pass: Strategic defense by aggregations of Pseudomyrmex spinicola (Hymenoptera, Formicidae) on the trunk of Acacia collinsii (Mimosaceae). Insectes Sociaux 55 (3):241-245.