#aphidinae

Oleander Aphids, Aphis nerii (by me)

As well as feeding on milkweeds, they both sequester the milkweed's poison, and advertise the fact with their bright orange and black colouration. Most animals that try eating a Monarch or an Oleander Aphid soon regret it. According to this page, spiders that survive the dose of cardiac glycosides from the aphid build strange disrupted webs. I identified the aphid with the help of Australian Critters, Larena Woodmore's website dedicated to the species that turn up in her garden - over 550 species of insect alone, so far. Alas, I can't seem to thank her, since the anti-spam paraphernalia appears to be borked. Here's a PLoS One paper about other ways the Oleander Aphids defend themselves, too.

Aphids on a sunflower on Flickr.