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..

Propagating lady's smock for orange tip butterflies

Lady's smock Cardamine pratensis, the native wild flower also known as cuckoo flower, is a food plant for the delightful ....

...... orange tip butterfly, so if you plant it in a wildlife garden there's a good chance that orange tip butterflies will breed there. The fastest and easiest way to grow the plant is to propagate it from leaf cuttings and now is the ideal time to do that.

All you need to do is to remove a few leaves from as close to the base of a plant as possible, then lay them on wet potting compost in a flower pot and keep this in a polythene bag. Open the bag every couple of days and spray the leaves and surface of the compost with a water mist spray, so that they are permanently wet.

After two to three weeks you'll see little white roots sprouting from the leaflet bases and sometimes from their mid ribs. 

Within another week shoots will begin to appear.

One leaf will often produce about twenty plants, with sometimes two appearing from each leaflet. When they are well rooted you can separate them into individual pots, then plant them out in the garden when they're well established. They like moist soil and will grow well in grass around a garden pond.

Occasionally double-flowered lady's smock plants appear in the wild and, since they set no seeds, these can only be propagated from leaf cuttings.

Orange tip caterpillars

Back at the beginning of June orange tip butterflies were laying eggs on Jack-by-the-hedge (aka garlic mustard, aka hedge garlic) in our garden and since then the caterpillars that hatched have been doing pretty well.

In their early stages the tiny caterpillars are pale yellow but after a couple of weeks ....

.... they become grey-green and are quite well hidden when they align themselves with their host plant's seed pods. At this stage the prominent hairs on their segments are each tipped with a tiny droplet of secretion, which I suspect is something that repels potential parasites, like ichneumon flies. It doesn't deter wasps though, which I have watched carrying away small caterpillars. I once watched a wasp chew a larger orange tip caterpillar in half and then carry each bite-sized chunk back to the nest.

All the butterfly books mention the cannibalistic tendencies of orange tip larvae, and the way in which this butterfly only lays one egg per inflorescence, but this year I've seen several hedge garlic plants with two or even three caterpillars eating seed pods in what was the same inflorescence, where the butterfly must have laid multiple eggs. I wonder whether this was due to the late flowering of the host plant and the need for the butterflies to lay a lot of eggs quickly. It may be that they are more likely to do this in plants like hedge garlic that produce a lot of large, succulent pods, unlike the alternative and much smaller food plant lady's smock, where the food supply from each inflorescence is much less.

A caterpillar like this, that's approaching maturity, easily demolished one of these three inch-long hedge garlic seed pods in a day. Then, when they are fully fed, the larvae vanish, crawling away to pupate. We've had a thriving orange tip colony breeding in the garden for many years and I have only once found a pupa, suspended from a dead plant stem by a silken halter and extremely well camouflaged, with an outline that resembled a thorn.

Orange tips

Today's Guardian Country Diary describes the way in which orange tip butterflies always seem to roost in the open, usually perched on a flower, when bad weather approaches - but always emerge miraculously unscathed after a rain storm has passed.

We've had a colony of orange tips in our garden for over twenty years. Apart from  butterflies that hibernate as adults - peacocks, commas and small tortoiseshells - they are always the first to hatch from overwintered pupae, just at the time when lady's smock Cardamine pratensis comes into flower. This is one of their caterpillars' food plants, but I've also planted the carnation-scented sweet rocket Hesperis matrionalis which they also breed on. The third caterpillar food plant is hedge garlic Alliaria petiolata, which the first female orange tips to emerge usually lay their eggs on. This can be a rather invasive plant if you let it run to seed but the caterpillars consume a substantial proportion of the seed pods.



The eggs are laid singly, either on the inflorescence axis (here on hedge garlic) or on a flower pedicel. They only ever lay one egg per inflorescence, because the caterpillars have cannibalistic tendencies if they have to compete for food.

The green caterpillars (see photo here) align themselves along the developing seed pods of the food plant, eating the pod from the tip towards its base, and in this position can be hard to spot.

What happens when a raindrop, travelling at terminal velocity, hits a butterfly .....?

I've never seen an insect actually hit by a raindrop but I did once read an eyewitness account (of dubious reliability) of such a collision with a bumblebee in flight, which supposedly killed the bee. It came to mind yesterday as a dark rain cloud slid over the sun while I was photographing this newly-minted female orange tip butterfly  visiting bluebells.

Almost immediately the butterfly folded its wings as completely as possible, assumed a vertical position on a bluebell infloresence and even aligned its antennae tightly in line with its body axis - all of which presented the smallest possible target for a falling raindrop. I wonder if this instinctive behaviour is triggered by the sudden drop in light level and temperature that's characteristic of an approaching shower on a spring day? Many insects crawl away under leaves during rain showers but orange tips always seem to roost in the open. I've often found dew-covered specimens early in the morning.

As soon as the sudden and very heavy shower had passed I went out to take a look and found the butterfly unharmed..... hard to believe that it hadn't been knocked off its perch by the downpour!

Hidden Defences?

Back in May I posted some pictures of the very egg that this orange tip caterpillar hatched from and since then, with its hedge garlic plant growing in a pot, I've been able to follow the progress of the caterpillar as it has muched its way through the seed pods. Now it's about two weeks old and growing fast. Its colour scheme provides natural camuflage when it aligns itself with the seed pods, but when I enlarged this photo I discovered something else that might be some kind of defence against predators. If you double click this image to enlarge the picture you should be able to see that almost every hair on the body has a small drop of liquid on its tip. This must have been secreted, because we've had blazing sunshine all day and this was taken in late afternoon - the water droplets didn't come from rain or dew. I wonder if the caterpillar secretes some obnoxious substance from those hairs, to keep parasites or predators at bay?  

Recovery

There are two reasons for posting this picture of the familiar orange tip butterfly. The first is that thirty years ago, when I first moved to the North East, this was an uncommon butterfly here. Seeing one was something worth getting excited about; now they are very common and even breed on lady’s smock, dame’s violet and Jack-by-the-hedge in my garden. The second is that this photograph, taken today of the first orange tip I’ve seen this year, newly emerged and pristine, was taken in urban Newcastle, on a grass verge beside the lower reaches of the Ouseburn, just before it reaches the Tyne. The lower Ouseburn was once one of the most polluted stretches of river in Britain and until the mid-20th. century was flanked by a devil’s cauldron of industries that dumped waste into its waters. Now it’s well on the road to recovery. I regularly see kingfishers there. So the orange tip shown here symbolises a wildlife good news story – the expansion of a butterfly’s range and habitat recovery. To read more about the Ouseburn’s history, visit http://www.ouseburntrust.org.uk/