Arthropedia - A is for Aphids

Introduction

There are over 600 species of aphid in the UK.

While some of them are listed as agricultural pests and can be a nuisance on garden plants (think of the ubiquitous ‘greenfly’ and ‘blackfly’ that can infest anything and everything from roses to broad beans), most are not problematic and they all form a very important part of the biosphere.

Variegated Oak Aphids (*Lachnus roboris*) and ants on an oak tree.

In the garden, if you grow a wide variety of plants and flowers to increase wildlife diversity, aphids are seldom a real nuisance.

Every year the spurge flowers in our garden get smothered in greenfly but the resident House Sparrows soon take note and snaffle up large numbers of them. One year we even had a Wren picking through the stems – a joy to watch just the other side of the living room window.

The Wren’s fine bill is adept at picking off small invertebrates although this fledgling in my local cemetery was probably winkling out spiders from the Yew hedge it was skulking around.

Love them or loathe them, aphids are fascinating insects. They are actually bugs, belonging to the order Hemiptera (sub order Sternorrhyncha). They feed by sucking sap from plant tissues, usually openly on stems or leaves but some species are found underground where they feed on plant roots and are known as root aphids.

Vetch Aphids (*Megoura viciae*) haven’t proved harmful to the Yellow Meadow Vetchling in our mini meadow.

Many species are parthenogenic (i.e. have fertile females that do not need a male to mate with) and females often give birth to live young, avoiding the egg stage. These offspring develop rapidly and are soon producing their own young, thereby quickly increasing the number of aphids in a very short space of time.

Some species secrete a waxy substance to help protect them from predation while others are attended by ants that act as bodyguards.

*Plocamaphis flocculosa* is an example of a waxy aphid.

While the lifecycles of economic pest species have been well studied, many other species are poorly understood and there is much still to be discovered.

The Giant Willow Aphid (Tuberolachnus salignus) for example is something of an enigma. As the name suggest, this is one of our larger species and it is often reported around late summer/early autumn when large colonies are suddenly noticed covering the branches of willow trees although it is to be found from July through to March. Numbers tail off by February and none have ever been seen from April to July. No males have ever been seen so the species is parthenogenic and they are known to give birth to live young so during the months when they are absent they aren’t simply sitting about as eggs. It is possible that they hide away in crevices in bark but no one knows for sure.

Giant Willow Aphids are distinctive enough to be instantly recognised.

While many species are polyphagus (meaning they feed on a variety of plants) others are restricted to species in a particular genus (e.g. oaks) or even one plant (e.g. Tansy) which can aid identification. Having said that, some other species have alternating generations that feed on different plants which rather complicates matters.

Honeydew and Ants

A colony of aphids on a pine tree being tended by Jet Ants (*Lasius fuliginosus*).

As the aphids suck up sap from their host plant, they exude a sugary waste product known as ‘honeydew’. Because of this many species are regularly attended by ants which are said to ‘farm’ them; the ants guard the aphids from predators and will even pick them up and move them around and in return ‘milk’ the honeydew from them getting a valuable food source.

As an interesting aside, bees also collect honeydew and ‘Honeydew Honey’ is available to buy. I’m not sure about eating something that has been voided out of the back end of an aphid, however sweet it is. But then actual honey is basically regurgitated pollen and nectar. If a human being was responsible for either product I don’t think there would be many takers for them.

Rose Stem Aphids (*Maculolachnus submacula*) on Sweet Briar in our garden with the common black garden ant *Lasius niger*.

Root aphids are also often found in association with ants, living inside their nests where they too provide honeydew. Here you may also find the Ant Woodlouse (Platyarthrus hoffmannseggi) which scavenges on waste products and other detritus in the nest.

Root aphids in a *Lasius niger* ant nest with ghostly white Ant Woodlice.

While aphids themselves are prey to other creatures, the honeydew they secrete is an important food for several of our butterflies and a number of hoverflies as well.

Honeydew on leaves also provides nutrients for various moulds / mildews to grow which are in turn food for other creatures (the 22-Spot Ladybird is one example).

Purple Hairstreak butterflies seldom come down from the treetops, preferring to sup up honeydew from leaves rather than taking nectar from flowers.

Aphid Predators

Entering the nosh-pit. Seven-spot ladybird and an aphid banquet.

A colony of aphids will attract a whole host of predators from other insects and spiders to birds.

Wasps are high on the list, especially social wasps (Vespula spp) which many people have a particular disliking for despite the fact that they eat so many so-called pest species, and also tiny parasitic wasps which leave behind the empty husks of their hosts.

The tell-tale empty aphid husk cocoon of a *Praon* species of parasitic wasp on the underside of an oak leaf.

Harlequin Ladybird larva polishing off an aphid.

Ladybirds are perhaps the best known aphid predators and as such they are a welcome friend to most gardeners, not only do the adult beetles eat aphids but so do their avaricious larvae.

Another example of an insect where both adult and larvae are aphid predators is the delicate looking lacewing. The larvae in particular are voracious, sucking dry each aphid and then often carrying the corpses on their back as camouflage to prevent them being eaten in turn.

A lacewing larva, well-camouflaged with the corpses of its victims, sizes up a potential meal.

Another ‘gardener’s friend’ are the hoverflies. The often colourful and pretty adult hoverflies mostly feed on nectar so are important pollinators and in many species the larvae prey almost exclusively on aphids.

Identifying Aphids

Identification of aphids is rather difficult, usually requiring a microscope and specialist keys to work through.

Immature stages can look different to adults and you often get winged forms as well as non-winged.

A few species are distinctive enough to be identified from good close-up photographs, helped by the fact that certain species feed only on specific plants. Some basic botanical knowledge is helpful here, for example I know when I’m looking at a willow but not necessarily which one!

Aphids on Larch. The host plant helpfully narrowed down the identification of these aphids to a particular genus and a closer look with a hand lens confirmed them as *Cinara cuneomaculata*.

Easily identified examples include the Giant Willow Aphid (mentioned previously) and the Tansy Aphid.

Both, as their common names suggest, are to be found on one host plant although in the case of the Giant Willow Aphid any species of willow will seemingly do. They are also morphologically distinct from other species of aphid.

The Tansy Aphid (*Macrosiphoniella tanacetaria*) is restricted to just one species of plant and is unlikely to be confused with any other aphids.

Even if you can’t identify the species of aphid you are looking at, it is worth watching them to see what predators are targeting them – you never know what fascinating arthropod may come along.

Despite its waxy coating, *Plocamaphis flocculosa* is easily identified from its general colouring, overall size and the bright orange siphunculi towards the rear of its abdomen.

Useful websites

For more photos of aphids, see my Aphids Gallery.

Influential Points: https://influentialpoints.com/Gallery/Identify_the_most_commonly_seen_British_aphids.htm

Nature Spot: https://www.naturespot.org.uk/family/aphididae.