November 2015. A member from Samoa asked about the mud wasps that are daily visitors to his home and leave the place in a mess. How can they be controlled but not killed. And what do they feed on?

It was likely to be the black and yellow mud dauber, Sceliphron caementarium. It is an introduced species, and feeds almost exclusively on spiders. Spiders are useful for controlling many pest insects in the home garden. As it is not a native species and it preys on so many useful predators, control efforts are not only keeping the home clean, but also helping to maintain the spider population. They are also newly introduced to Tonga. They may have come with personal effects, ships’ containers, etc.

In the Cook Islands there are several mud-nest wasp species. The photo (below) shows the mud-nest wasps and three of their known spider prey. This image is from this link: http://cibedev.scizone.net/cibed/dbs/results.html?t=mason|keyhole|dauber|Pison|Asian|Neoscona|Thorelliola&c=1,36,37&o=1,All,images (you can click images to expand).

The two Sceliphron wasps make the largest nests and traditionally are full of the large orb-web spider Neoscona. Gasteracantha (Asian Spinybacked Spider) arrived here in the 1990s and on each island it was initially very common. On Atiu and Mangaia there was then a notable decline and Sceliphron nests were full of the spider.

A small dark Pison sp. had a nest full of the small jumping spiders: Thorelliola. The nests of Anterhynchium, Odynerus and Pachodynerus were all full of small caterpillars, about equal in length to the wasp itself. Although the nests can be annoying, these wasps do help to control various moths and spiders.

Another member made the point that not all wasps that make mud nests prey on spiders. The photo above (top) is a Zeta sp., family Eumenidae, that was caught in flight carrying a tomato looper to its mudcell in Trinidad, West Indies. Five cells were opened and all contained living but paralized caterpillars, together with an egg (the latest, freshly closed cell) or a wasp larva in increasing state of development. The fifth cell contained a pupated larva.

Overall, members were intrigued and impressed by the ability of these wasps to build and stock their mud cells with food for their young. Do not kill them!

Later, the farmer who asked the question sent a photo of the larvae found inside a dauber cell. There were 25 larvae altogether – 23 captured caterpillars and two dauber grubs or larvae in this 2×2 cm cell.