Urban Purple Hairstreaks

I had a most unexpected and delightful walk to work this morning. As I was about to cross Westbourne Avenue, where a water leak has been repair, a passer-by flushed a small butterfly from the barriers. I thought it was probably a Holly Blue, but when it settled with wings closed on a privet hedge nearby, I realised it was a hairstreak! I fumbled for my camera as it fluttered along the hedge into a front garden, where it sat with wings open. With shaking hands, I was able to take a photo (below), confirming the id as Purple Hairstreak! 

The first Purple Hairstreak

The Avenues is a very leafy part of Hull, with large gardens often holding large trees. In fact, there is a mature, spectacular oak at the back of the Adult Education Centre on Park Avenue not far away, and, as I walked past, I wondered if the wind might have blown the small butterfly away. I carried onto Jack Kaye fields. A Speckled Wood by the entrance to the fields, by an oak, reminded me to do a butterfly count, and I set an alarm on my phone to 15 min. I counted six Speckled Woods, as they squabbled around the trees. Then I moved onto the first glade. A small butterfly settled on a Whitebeam to bask in the sunshine. As I focused my camera, I got the feeling of being in a dream: it was another Purple Hairstreak! It has its wings closed and I took plenty of photos. 

Tree canopy butterflies

Purple Hairstreaks are canopy specialists, they spend much of their time on tree tops, around oaks (the larval food plant) and nearby trees, where they feed on honeydew. Although other species that obtain most of their food from honeydew, like Speckled Wood and Holly Blue, can occasionally be found feeding on flowers, or resting or fluttering low down, Purple Hairstreaks rarely come down to the lower level of trees, but they have been seen feeding on bramble or hemp-agrimony. They live up in the tree tops, and it is for this reason that they are easily missed. There are only 18 records of this species in East Yorkshire, mostly in nature reserves, but also at Snuff Mill Lane, just outside Hull, where I saw them in July and in Beverley Westwood, which has a sizeable population. They are not only found in woodland, but also along lanes and in parks with oaks. But, as these lovely, tiny butterflies, spend their adult lives up in tree canopies gorging on honeydew, they are likely to be overlooked and under-recorded. In the last few weeks I've been looking for them at Jack Kaye, staring into that small oak by the entrance, so although I was beyond pleased to find it, I was a bit astounded that it had actually happened. 

I will keep an eye on this area to check if these are isolated individuals or if there is a colony, and I plan to keep looking at oaks, wherever they are!

Brown scale insect

A garden ant stimulated this scale insect to produce honeydew with her antenae. Some these scale insects, Parthenolecanium corni, are growing on a grapevine branch, just under strips of bark. They are about 5 mm, dark and shiny, with ridges across. When young, they are tiny and mobile and are called crawlers, and live under leaves. When they are ready to moult into the immobile scale stage they move into branches. Scale insects, as aphids, suck the sap of plants, and excrete a sugar rich liquid call honeydew, which ants like.

 These scale insects can become a pest of various fruit trees. The scale insect has natural enemies, though. Parasitoid wasps inject their eggs into the scale insect, and the larvae will emerge though holes in the scale, instead of the crawlers. A parasitised scale insect after the wasps emergence is shown below.

26/12/2011

Elder aphid networks

The photo above shows a dense colony of Elder aphids, Aphis sambuci, many individuals of different ages feeding close together. They are likely to be all a clone, female descendants of a single founding female that emerged from an egg early in spring, and identical genetic copies of her. Elder aphids forms this characteristic ash grey patches on tender elder stems. The aphids suck the elder sap using their piercing mouthparts. Having a close look at elder aphids gives you an opportunity to learn to learn about ecological networks in a few minutes of observation. All the photos in this post were taken in the space of seven minutes this morning on my way to work on the same young elder bush.

 Despite the fact that elder, Sambucus nigra, has relatively few insect predators, most likely due to it having cyanogenic chemicals in its leaves, elder aphids are an important link in networks making use of elder sap. 

Ants have a mutualistic relationship with the aphids. They benefit from the aphids honeydew by soliciting them to excrete it, taping them with their antennae. The sugary rich liquid is consumed by the ants and their larvae. The ants treat the aphids as their domestic animals. The aphids benefit too, as potential predators or parasites are pursued or attacked by the ants.

But the ants can't totally defend the aphids from their numerous predators. Here a female hoverfly, Epistrophe eligans, lays eggs on a patch of elder aphids.

A hoverfly egg is visible on the centre of this photo, on the edge of the aphid colony.

See the patches cleared of aphids in this patch? They are due to predation by the green hoverfly larvae just visible amongst them. Surrounded by food, the larvae will gorge on the aphids and grow rapidly.

This hoverfly larvae (possibly Epistrophe eligans) is likely to be ready to pupate.

Not only hoverflies, ladybirds are attracted by this aphid bonanza and adults land on the elder, possibly attracted by the smell of aphids. A Harlequin sunnies itself on a leaf...

...while an active 2 spot searches about.

Ladybirds have laid their bright yellow egg clutches on or under the leaves, near the aphid colonies.

...here visible on the background. I couldn't find any ladybird larvae today on this elder. 

This fly enjoyed licking the honeydew on a leaf. Some species of butterflies, like the Speckled Wood, also takes advantage of honeydew.

Five species (2 ladybirds, a fly, an ant and a hoverfly) thriving on elder aphids. If I had waited a bit longer, or being a bit luckier, I could have witnessed tiny parasitoid wasps that lay their eggs inside the aphids and eat them from the inside!