Purple Hairstreak caterpillar found in Hazel nut shell

View of Hazel nut shells with one half shell containing a pre-pupal caterpillar
Pre-pupal Purple hairstreak caterpillar found in a half shell of a Hazel nut Photo: Wren Franklin

Wren Franklin has sent us an amazing picture of a Purple Hairstreak caterpillar found in a Hazel nut shell by his three and a half year old son.

Purple Hairstreaks, though not uncommon, are often overlooked.  As an adult they spend the majority of their lives high above the ground in Oak and Ash trees where they are usually seen as little more than silvery flecks and silhouettes against a summer sky.  However, although adult, egg and larvae are largely arboreal the final instar caterpillar descends from the tree to pupate at ground level.  Imagine my surprise when, on a recent woodland walk near Milton Abbas, my three and a half year old son eagerly presented me with a fist full of Hazel nut treasure and nestled neatly in a half shell was a pre-pupal Purple Hairstreak caterpillar.

What are the chances? After a good look and a few photographs we positioned the shells back where they had been found – on a stump, below under story Hazel, beneath high canopy mature Oaks.   The literature sheds some light on the pupation of this species. Firstly, we can tell that the caterpillar in the nut shell is close to pupation due to the absence of the chevron markings that are so striking during the third and fourth instars (seen in the image of the only other Purple Hairstreak caterpillar I have seen away from Oak foliage).

It is also known that this species has an association with ants, with Jeremy Thomas reporting finding pupae in ant nests near the base of Oak trees.  I wonder what percentage of caterpillars are found by ants and how many successfully pupate and avoid predation elsewhere.  Certainly donning a wooden suit of armour appears a good strategy.

Remember to cast your gaze up to the top of any sun-bathed Oak on late afternoons during late June and early July to catch a glimpse of one of our more easily missed butterfly species.       

This article was written for us by Wren Franklin and we would like to record our thanks to him for this.

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