Friday, June 23, 2017

Froghoppers























Throughout June many of the plants in the garden have been decorated with 'cuckoo spit', the frothy bubbles blown by froghopper nymphs feeding on the sap.



















Outside of their bubble bath, the nymphs are cute little insects .....


































.......with lethargic movements, strange, two-toed feet........






















.... and a bulbous nose, which acts as a pump when they suck sap through a stylet that punctures the plant.


































Now the nymphs are beginning to turn into adults and they are incredibly energetic, leaping through the undergrowth with tremendous speed at the slightest touch.

An adult froghopper can catapult itself to a height of 140 times its body length. That’s equivalent to a human jumping over a bar set at 260 metres, when the current Olympic record stands at 2.39 metres.

In 2003 Cambridge neurobiologist Malcolm Burrows, analysing a theoretical  high jump contest between fleas and froghoppers, found that the latter coming out on top. Eleven percent of a froghopper’s body mass is concentrated in two jumping muscles but these can’t contract fast enough to generate the insect’s take- off acceleration of four metres per second in the first millisecond of its jump. That’s achieved with a leg-locking mechanism which, when it breaks free, releases a force of over 400 times the body weight of the jumper, over 130 times greater than human’s legs can manage.  The key to this performance is resilin, the most efficient elastic protein known,  which stores energy accumulated by the insect’s contracting muscles and releases it with explosive force, generating acceleration of about 400g; we humans black out under a force of 5g. 

The adults of Philaenus spumarius display a range of colour patterns. Many are just plain brown but this individual sported a smart two-tone colour scheme.

Monday, June 19, 2017

Orange tip caterpillar food plants





















We have all three of the commonest food plants for orange tip butterflies in the garden - hedge garlic (Alliaria petiolata), lady's smock (Cardamine pratensis) and sweet rocket (Hesperis matrionalis), though I only encourage the last two because hedge garlic is so invasive.

This year, for the first time, I've noticed the caterpillars feeding on the developing fruits of this plant, honesty Lunaria annua.

I think they probably find it tougher to chew than the other three plants but they seem to be growing rapidly on this diet.


















The only drawback, from the caterpillar's point of view, may be that they are more conspicuous on these disk-shaped fruits. When they align with the long, thin pods of the other three plants they are quite hard to spot because their countershading colour scheme works very well in those circumstances and they don't cast a bold shadow..




Saturday, June 10, 2017

Barn owls


It used to be the case that you could go for years in my part of Durham without seeing nesting barn owls. This week I've had the pleasure of watching two pairs.

The first was a bird hunting over open rough grassland, with scattered hawthorns, beside an old railway line that is now a public bridleway.

Barn owls almost seem to float across the ground, then suddenly perform a wing-over and stoop on their prey. This one struck three times before it rose with something small and furry in its talons, flew high over the trees and headed towards some old farm buildings where it must be nesting.

The sighting of the second pair was very close to home, nesting in a hollow ash tree on a farm belonging to a friend. She has farmed there for over forty years but this was the first barn owl that had ever graced them with a nest, so she was absolutely delighted. 

I spent yesterday evening watching a parent bird flying to and from the nest, hunting over the pastures amongst the cattle at sunset. Sometimes it flew right through the orchard where I was standing, no more than twenty metres away.

A magical evening, watching a truly stunning bird.