Dandelions – an early food bank

May 14th 2020

Dandelions – an early foodbank

For several years, I have been trying to cultivate a wild garden in Torbreck (NC0824) in order to attract insects and other wildlife.  Consequently, I have been encouraging plants such as dandelions (photo 1), which some people regard as weeds. However, they are rich in nectar and pollen, within easy reach of insects with short tongues. Nectar provides energy and pollen provides protein which adult insects require to mate and lay eggs.  On 25th April 2020, in the space of a few minutes, I noticed four different species feeding on dandelions.

The first was a Small Tortoiseshell butterfly Aglais urticae, newly emerged from hibernation (photo 2).  Once mated, the female will lay eggs on young nettles in full sunshine, 60 to 100 at a time. The caterpillars which hatch out after 10 – 14 days live communally inside a web of silk, emerging to bask and to eat.  After their last but one skin moult, they then disperse and eventually pupate. The adults which emerge later in the summer will then hibernate in places like sheds, attics, hollow trees and caves.

A few mining-bees, probably the Orange-tailed Mining Bee, Andrena haemorrhoa stayed for longer periods on the flowers (photo 3). These tiny bees nest in holes in the ground in south-facing banks. Bees of the Andrena genus are important hosts of the Oil Beetle Meloe violaceus, adults of which are seen on sunny days in spring in Assynt (photo 4).

Oil beetles mate soon after emergence and the female lays about 1,000 eggs in a short burrow in the soil.  In her lifetime of about two months, she can lay 40,000 eggs.  The emergent larvae, which are called triungulins (photo 5), climb up vegetation and sit on flowers, waiting for a lift from any insect which visits the flower.  Those that survive are taken back to the nests of mining bees, where they eat the eggs and pollen of the host bee.  They pupate in the nest and emerge as adults the following year.

And still they came!

Next, I managed to photograph the hoverfly Eristalis pertinax (photo 6). The species in this genus are described as bee mimics, but most are not convincing.  However, an interesting feature is that Eristalis larvae are aquatic and are called rat-tailed maggots.  Adult females lay eggs in wet decaying vegetation in ponds and ditches.  The larvae which hatch out have ‘tails’ which are telescopic breathing tubes enabling them to live on detritus at the bottom of a pool while still breathing air.  A few years ago, I found these larvae in a temporary pool on top of a hill opposite my garden (photos 7 & 8).

Lastly, the most abundant visitor of all was the Northern White-tailed bumblebee Bombus magnus (photo 9). The fertilized queens emerge from hibernation at this time and forage heavily on dandelions and garden shrubs like flowering currant. They set up nests in old rodent burrows, lay eggs in cells and feed the larvae on pollen.  The first brood produces worker bees which then raise further broods consisting of males and new queens.

Dandelions also provide food for birds.  As I write this in the second week of May, I have twice observed a goldfinch and a greenfinch eating seeds from the closed flower heads (photo 10).  So, in just a short time, dandelions have proved very useful for six different species and, no doubt, for many, many more.

Words and photos, other than no.5, Gwen Richards

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