Cycling, macintosh, natural history and life in Singapore - Archives
Mon 29 Aug 2005
Potter wasp at the door, Part II
Category : Singapore Naturalist
Sat 27 Aug 2005 morning - With at least three large caterpillars inside the second cell (see Part I), its filled it to the brim. Why hasn't the second cell been sealed? The first one was sealed by two days. It has been three days already.
The caterpillar nearest the mouth of the cell is twitching energetically, much more than expected. Not a pretty sight!
Sat 27 Aug 2005, after 3.00 pm - That afternoon, the door is opened to reveal a fallen caterpillar just below the nest. Unfortunately it is stepped on, bleah! The heavy twitcher must have been resistant enough to the venom to twitch its way out of the unsealed cell!
Early that evening, after 6.00 pm, I realise the second cell seems only to contain one caterpillar - a far cry from the filled nest of the morning. Another caterpillar must be missing!
Sure enough, more than a metre away down the corridor, another caterpillar is discovered, surrounded by ants. What's going on?!
All the colours observed in the nest chambers are explained by the body patterns of the caterpillar. The green colour, however, is special and comes from the fluid-filled enlargement of the thorax. The thorax is the predator's usual point of attack, so presumably this deformity is the result of the wasp's paralysing injection of venom. I pop the two caterpillar bodies into a sealed plastic bag and then into the freezer soon after as ants are swarming around it - the bodies are at least a few hours old.
Did the energetically twitching caterpillar finally fall out of the cell by twitching hard enough? This seems likely, given that the caterpillar was found just below the nest.
Did the other caterpillar twitch-crawl all that way down the corridor? Could it have been that resistant to the paralytic wasp toxin? Possibly.
Or could another potter wasp have raided the open cell, but lost its grip of the heavy caterpillar on the way out (I don't know if this happens with potter wasps)? Could the returning mother have dropped a fresh caterpillar? I favour the idea that the caterpillars escaped. Ants would have got to them both in the end - they were doomed once the potter wasp grabbed them from their feeding frenzy off some leaf.
Why the nest had not been sealed remains a mystery. The mother wasp had all of Saturday morning and afternoon to seal the nest but didn't. Has the nest been abandoned or the mother killed?
Sat 27 Aug 2005, after 7pm - The cell seems rather empty; certainly there is less than half the prey of the previous night. If the mother does not return, the grub that hatches will go hungry after devouring the first caterpillar.
I peek into the nest and see a sliver of a white larva. Foreboding thoughts of an abandoned nest make me think of the maggot of a flesh-eating fly, freshly hatched out to devour the remaining caterpillar and the wasp egg! Then I realise maggots are not usually solitary and feed on dead meat not living flesh - well most of the time at any rate; I am being silly.
Then it dawns on me, that Saturday night - I am looking at the newly hatched potter wasp larva of the second cell!
It's so small, and is dwarfed by the lone snack in the cell, the caterpillar that did not get away. But being an insect larva, it will feed voraciously and grow in leaps and bounds. In the adjacent cell, is its sibling, who must be munching away in programmed determination.
The escaping caterpillars have left the potter wasp trapped in a cell with insufficient food. It could starve to death after it has eaten alive the remaining caterpillar.