I live in Cairns, North Queensland, Australia. I have just found an ant that continually cast off from its location using a strand of web, much like a spider. My partner and I were unable to find any information on such an ant on the web, so were wondering if you could point us in the right direction? Any guidance you could give us would be much appreciated.
Thanks so much for your question! It is possible that what appears to the unaided eye to be an ant is actually a spider! Many groups of spiders (and several different types of insects as well) have evolved the appearance of ants, either to fool ants into letting them close enough to eat them, or capitalize on ants' cooperative reputation to intimidate potential predators.
The behavior you described sounds like a spider in the 'jumping spider' family, the Salticidae. They will often jump, and leave a 'dragline' of silk as a way of ensuring they have a place to retreat to if they end up jumping too far, or over a cliff that was higher than they thought. I have found that these mimics often switch between moving in a very convincingly ant-like fashion, and reverting back to their jumping spider style of movement.
The largest and most diverse group of ant mimics is the jumping spider genus Myrmarachne, with more than 200 species. The center of diversity for this group seems to be in Southeast Asia, although several species also occur in Australia. Several other genera of spiders also mimic ants, though, both jumping spiders and otherwise.
Here is an excellent link with many pictures and natural history information on jumping spiders in Australia:
Here are some pictures of one of the most common genera of ant-mimicing Salticids in Southeast Asia and Northern Australia (pictures taken in Malaysia).
A google image search also lead me to this amazing picture, posted on Flickr
Spiders aren't the only ones to have evolved ant-like appearances. Several groups of insects, including beetles, flies, and praying mantids, have independently evolved ant-like shapes and colorations. Some insects with larger adult phases only resemble ants when they are very young, and some jumping spiders actually seem to resemble different ants at different ages. Ant-mimicry, or "myrmecomorphy" was extensively reviewed by McIver and Stonedahl in this 1993 paper here, and the wikipedia article on ant mimicry has some more interesting information
Hope this helps!
Jesse Czekanski-Moir & the AntAsk Team.