Balcony beasties – cabbage whites and their enemies

It is true you do not have to go far to see wildlife, even in the midst of a big city. Invertebrate scholars are particularly fortunate in this regard as insects, arachnids etc. really are everywhere, in your home and even on you. Here in my student room in Earls Court, London I have a little balcony which I have used to grow salad and tomatoes. Being an entomologist I soon became more interested in the creatures eating my vegetables (and eating them!) than the produce.

I watched a large white (Pieris brassicae) lay clusters of eggs on my kale a couple of weeks ago. Now if i was a ‘proper’ gardener I would remove these but as an entomologist I take pleasure in watching them develop so don’t begrudge them my salad. The caterpillars hatched and grew rapidly, first feeding together then spreading out on the container of plants. I later found a single small white (Pieris rapae) caterpillar which I had missed, as these are laid singly and must have been overlooked.

Large White caterpillars feeding on my kale on the balcony

Small White caterpillar (note the leaf mines on the kale, I will discuss these in another post)

By early August they were ready to pupate but I have only found on successful pupae, the rest being devoured inside out by the braconid wasp Cotesia glomerata.

The only successful large white pupa

All but one of the infected caterpillars mostly moved away from the food plant, climbing up the balcony to find a place to pupate, instead the braconid larvae emerged from the caterpillars and spun silk cocoons, the moribund caterpillar remaining attached and hunched over the cocoons. The caterpillars were still alive for sometime after the parasitoid larvae had emerged and pupated.

Cotesia glomerata larvae emerging from large white caterpillar, this one remained on the food plant.

Caterpillar on the side of the balcony with Cotesia glomerata in their silk cocoons underneath.

The small white caterpillar had a different fate, though no less gruesome. I woke up one morning to find it being macerated and carried of piecemeal by a wasp. Amongst the remains it could be seen it was also infested by Cotesia glomerata larvae.


The next balcony bugs post will focus on the flies in my vegetable garden.

A weekend of hoverflies

This weekend I was at the Field Studies Centre at Preston Montford in Shropshire to learn about hoverflies. This is the penultimate course in my University Certificate in Biological Recording and Species Identification run by Manchester Metropolitan University. The course is run by Roger Morris and Stuart Ball of the Hoverfly Recording Scheme and I had previously attended their 2 day course which I enjoyed very much so I came back for more!

The course started with an introduction to hoverflies and how to recognise them, Roger and Stuart always emphasise the importance of understanding the ecology of larvae, which are often understudied in invertebrate groups. Hoverflies have particularly diverse larval biologies, with examples from all modes of life except parasitism and unusually for flies are relatively well studied, with the larvae of around two thirds of the UK's 282 species known; there is even an identification guide on them, now sadly out-of-print - the Colour Guide to Hoverfly Larvae: Diptera, Syrphidae by Graham Rotheray.

The next day began by going through some of the the keys and learning the characteristics of the different tribes, good revision for me and I am finally able to find my way around wing venation.

A hoverfly wing - R-M is your friend

Based on © Hans Hillewaert / CC-BY-SA-3.0 via Wikimedia Commons

You see the first time I came across wing venation in a key I found it very confusing, the wings just seemed to have a mass of different veins branching all over the place and trying to work out which were which was tricky. In hoverflies at least, a useful tip is to find the radial-medial (or R-M) cross vein, which is quite prominent in the middle of the wing and crosses the vena spuria or false vein (actually a deep fold), particular to hoverflies. This immediately locates the radial 4 + 5 vein which runs along the top, the discal cell which lies underneath and the first basal cell which it forms the outer border of. Now venation is not so daunting!

On the Sunday we were allowed out of the lab to see what hoverflies could be found around Preston Montford field centre which were then brought back for killing, pinning and identification. A few other diptera groups sneaked in as well!

My modest catch, well I had a MSc thesis to write!

The final day comprised a test towards the uCert qualification which I passed. Hopefully I will also pass the 2nd assignment and then I am just one more identification course away from the Certificate!

Thanks to Roger and Stuart for another expertly run course!