March 1996
The Suffolk Argus
Holly Blue larvae and Black Garden Ants .................... by DouglasHammersley
Blackgardenant stimulating Newcomer'sgland
Fig. 1
In 1990 I planted two small holly bushes in my garden with a view to attracting Holly Blue butterflies (Celestrina argiolus). One bush, Ilex aquifolium "Golden King", is a female holly (despite its name) and the other is Ilex aquifolium "Silver Queen", a male plant. Both bushes are about one metre tall and they have proved to be excellent for observing and photographing the development of Holly Blue larvae and their association with black garden ants, Lasius niger. I soon came to realise that, in the male plant, the larvae feed on the young leaves but in the case of the female plant, the emerged larva feeds on the immature berries by burrowing its head into the berry and eating its contents from the inside. When the larvae are very small they appear to be disregarded by the patrolling ants but as they develop, the larvae are regularly attended by ants. The ants merely attend a larva and make no attempt to diven it or influence its progress when it moves around its host plant. Usually, one or two ants act as outriders and one or two others ride on the larva, often showing particular interest in the caterpillar's seventh segment where Newcomer's gland is situated. This gland is seen as a small, transverse invagination which can be stimulated to secrete a kind of "honey-dew" on which they feed. Ants are seen to use their antennae to drum around the gland and cause it to open and secrete (see Fig. I).
-Site of right tubercle
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Head of larva biting hollyleaf
jJ
V
We worked our way up the gentle slope of the Benfleet Downs towards our next quarry, the elusive White-letter Hairstreak. Graham knew that they were already on the wing following a mid week visit when he was preparing for the walk. A thistle head provided our first White-letter Hairstreak of the day. With forewing tucked in behind hindwing they can be quite difficult to spot unless you are very close. The sickly sweet smell of Privet in flower nearby held at least half a dozen of these butterflies for our close inspection. One observation I have made is that once this butterfly has come down to feed it seems to allow very close inspection and even if disturbed it will often return to the same flower after a short while. Another patch of Bramble had a double figure number of this species feeding. By the time we left this area twenry to thirty had been counted, many times more than the total seen in Suffolk the previous year. Graham recalled that he had counted two hundred in one walk alone. There can be no doubt that this Park must be one of the top sites for this species in the country. The afternoon would again bring us into contact with the park's Marbled White colony. On our way down towards the railway line a Red Admiral (Vanessa atalanta) gave us a brief display as we approached the long grass which seemed to be an ideal area for the Marbled Whites. Graham said that the females drop their eggs to the ground from above the long grass. In this area we counted at least six more of these insects. They also seemed slightly more camera friendly than those we had seen earlier, probably due to the lack of sunshine. The long grass also yielded an unexpected surprise, Great Green Bushcrickets, not something you would wish to handle as I understand that they can deliver a painful bite. Conditions were fairly overcast as the group made its way back to the car park.
We stopped for a few minutes in front of some Oak trees and gazed upwards to see if we could add Purple Haitstreak (Quercusia quercus) to our growing list. Although there was movement high in the trees it was difficult to be cenain that these were indeed Purple Hairstreaks. The other likely species was Speckled Wood (Pararge aegeria) as we could make out that some butterflies were bigger than others. Back at the car park the final species count for the day was eighteen although this did include at least three seen from distance. The Suffolk members enjoyed the chance to see Marbled White, a butterfly not resident in this county and also White-letter Hairstreak, an increasingly rare insect in our area. Joint meetings like this are an excellent way of learning about the flora and fauna of the site. It is also good to exchange views and ideas with other branch members. Thanks again to GrahamBaileyand the Cambridgeshire & Essex branch members for showing us around an area they must be very proud to have in their County.
White-letterhairstreak (StrymonidiaUJ-album)
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