Butterflies of the Week 6th May 2020

  

          

Large and Small whites:  These are the ‘Cabbage Whites’ that are a gardeners’ nightmare. There are two separate species the Large and the Small. They both over-winter as pupae formed at the end of August or beginning of September and emerge in April the following Spring.

The Large White lays eggs in batches, particularly on the leaves of domestic Brassicas, up to 150 at a time. They hatch into caterpillars that feed particularly on the outer leaves of ‘cabbages’ and, being so exposed, their bold black and yellow colouring indicates to predators their unpalatability. There is some help for gardener’s in the form of the ichneumon wasp, Cotesia glomerata. These wasps lay between 15 and 80 eggs into young large white caterpillars. These wasp larvae feed on the caterpillar’s fat reserves without killing it and finally, when fully grown, break out of the now dead caterpillar forming a collection of yellow cocoons around the corpse.

The Small White lays its eggs singly and the caterpillars move onto the underside of leaves in the heart of the plant doing considerable damage. Being green in colour and being on the underneath of leaves makes them well camouflaged. In the same way as for the large white there are a variety of parasitic wasps (including Cotesia rubecula) that lay eggs inside young caterpillars.

To tell these whites apart look at the front edge of the forewings. In the Large White it goes all the way around the point of the wing as unbroken black. In the Small White the black is almost entirely on the front edge of the wing. Large White females and males and females of Small Whites have two more or less conspicuous black spots on the upper surface of the forewing. Male Large Whites have no such spots. Generally, the Large Whites are distinctly larger than the Small Whites, but they can each vary being extra small or large in size. You might think of Large Whites as being Peacock sized and Small Whites as being Small Tortoiseshell sized.

For both these Whites there are 2 generations each year with the butterflies flying in April and May laying eggs that become the butterflies flying in July and August whose eggs will go on to produce the overwintering pupae.

Photos   Peter Bright   Mick Fletcher

 

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