Wasps

What are Wasps & how to get rid of them 

There are many species of wasps in a range of sizes, colours and shapes. Some are beneficial in the garden and help control various insect pests. Others can be serious and destructive pests themselves. In large numbers, they threaten native insects and spiders, as well as Monarch butterflies. Monarch caterpillars are a tempting source of “protein” that wasps use to feed their young, so it's good to protect them by eliminating wasp nests.

There are 2 species that are of particular nuisance in and around the home and garden including the German Wasp (Vespula germanica) and Common Paper Wasps (Polistes spp.). Both look similar, however there are noticeable differences.

The German Wasp is an introduced environmental pest species. Worker wasps are 12–15mm long (queens and males are 20mm long, but it's very rare that you'll see them). German Wasps are very bright yellow and black, with their abdomen lined with yellow and black banding with distinct black triangular markings at the top of each band. They have a pair of black antennae, 3 pairs of yellow legs and 2 pairs of transparent wings on their back. 

Paper Wasps - also an introduced species to New Zealand - are generally tan-coloured with darker stripes, 10 – 15 mm long and narrower than the German Wasp.

There's also another newly introduced wasp called the Asian Paper Wasp (Polistes chinensis) (see image below). This species is often confused with the German Wasp, but the Asian Paper Wasp has less distinct yellow banding and more prominent black banding, plus it doesn't have the black triangular markings. These wasps are longer and narrower, and have yellow antennae. The Asian Paper Wasp is also less aggressive than the German Wasp, with nest structure and habits more akin to the Common Paper Wasp.

Wasps defend their nest aggressively, swarming out to attack if disturbed. Unlike bees that die after only one sting, wasps can repeatedly sting and remain unaffected. Their sting is painful and inflammatory. Multiple stings, or a sting to the throat, can be dangerous. Some people are allergic to wasp stings and may even be unaware of their allergy. Always use extreme caution near nests. 

Best Treatment for Wasps 

• Knockdown sprays and nest treatments are the best control for wasps and their nests.
• Blitzem! Wasp Killer & Nest Destroyer Aerosol Spray is a knockdown spray which also destroys the nest. 
• Treatment of the nest should only be carried out at night or in the very early morning when all wasps are present on the nest and are significantly less active.
• Wear Personal Protective Equipment (PPE): thick clothing which covers your entire body and is buttoned at the wrists and throat, goggles, securely fitting thick leather gloves securely fastened at the wrist, a hat and a bee-veil.
• To help see the nest at night, use a torch covered in red cellophane, as wasps cannot see red light.
• Once all wasps have been killed and the nest has been destroyed, place the nest into a plastic bag, seal well and place into the rubbish bin.
• Report German Wasp nests to your local council to help stop the spread of this invasive species.
• If a German Wasp nest has reached an unmanageably large size, for your own safety, please contact your local council and seek advice.
• Do not approach wasp nests unnecessarily.
• For multiple stings, a sting in/to the throat or if allergic to wasp stings, seek urgent medical aid. Otherwise, apply an ice pack and/or anaesthetic spray.

Nesting

Most German Wasp nests are located underground, some build nests in rockeries, tree stumps, and man-made structures such as wall cavities and roof voids. Nests are round and are made of chewed wood fibre, giving the appearance of muddy paper-mache. Nests range in size from 15 centimetres in diameter and reach up to an enormous 5 metres. German Wasp nest populations may reach into the many thousands making it very important to control populations early-on in infestation to avoid populations from getting out of control. If a nest has reached an unmanageably large size, for your own safety, please contact your local council and ask for advice.

The Common Paper Wasp has a small, papery nest with a distinct honeycomb structure. Nests are made from a mixture of chewed wood fibre and saliva. Nests can reach up to 10 – 12 cm and can be found hanging from horizontal surfaces such as underneath window sills, eaves, awnings, fence capping and in shrubs and trees. Nest populations are generally between 12 and 20 wasps. 

Habitat

German Wasps and Common Paper Wasps are active and feed during the day. At night, being social wasps, they can be found congregated at their nest.

German Wasps are mostly scavengers and feed on meat and other sweet foods. German Wasps are so prevalent near homes as they are attracted and feed on pet food, and human food and drinks. If wasps are observed in the area, do not leave food and drinks (especially soft drink cans) unattended or uncovered.

Common Paper Wasps, unlike the German Wasp, are not attracted to human foodstuffs. Juveniles are fed on a diet of caterpillars and other insects, while adults primarily feed on nectar from flowers and are an important pollinator. 

Lifecycle

German Wasp colonies start in spring when a single mated wasp queen constructs a small nest and lays her eggs. Eggs hatch into grub-like larvae, which develop into pupae. The queen tends the immature stages until they emerge as worker wasps (sterile females) in late spring/early summer. The first batch of worker wasps take over nest construction and rearing of larvae while the queen lays eggs. Over the summer, the nest grows in size and the population increases, reaching a peak in early autumn, when male wasps (drones) and new queens are produced. The new drones and queens mate and fly off to start new nests, perpetuating the spread of this invasive species into new areas and the environment.

In it’s native habitat in Europe, German Wasps tend to decline and die out over winter. However, in a warmer climate, nests may survive the winter and continue to develop over a number of seasons. This can result in giant nests of tens of thousands of wasps.

The life cycle of the Common Paper Wasp is similar to that of the German Wasp, except that nests typically contain only 12 to 20 individuals.

Natural enemies

Natural enemies of wasps include praying mantis, robber flies, other wasps, centipedes, spiders, lizards, frogs, birds, bats, mice and rats. 

Beneficial Wasps

While some wasps are pests in and around the home and garden, there are many wasps that are beneficial, including parasitoid and predatory wasps.

A parasitoid wasp is a female adult wasp which lays an egg on, in or near a host such as a scales, caterpillars, whiteflies, mealybugs, flies, weevils, grasshoppers and other wasps. The wasp egg hatches into a grub-like larvae and feeds on it’s host, eventually killing it. Wasp eggs which are laid inside the host, at the end of feeding, pupating and exiting, leave behind a skeletonised host body, a common example is mummified aphids. A very gruesome process, but effective nonetheless.

A predatory wasp is a wasp which catches, kills and feeds on it’s prey, whether to feed on the prey itself or to feed the prey to it’s young. Wasps feed on other animals such as caterpillars, moths, soft scales, and spiders.

Wasps can also be pollinators as they feed on nectar from flowers. Pollinators are a real asset for fruiting plants in the garden and are essential for the environment. 

What plants are impacted by Wasps

Wasps may occasionally chew marks in soft fruit, however most plants are unaffected by them. Some wasps feed on nectar which is beneficial to plants and is in no way detrimental to plant health. Other wasps are carnivorous (such as predatory wasp or parasitoid wasp) and eat various other wasps, insects and spiders. There are also wasps that are scavengers which feed on meat and sweet foods. 

How to prevent German Wasps appearing

• Avoid eating outdoors when there are signs of German Wasps.
• Do not leave food or drinks (especially soft drink cans) unattended or uncovered. Wasps have been known to enter an open drink can and may then be swallowed accidentally.
• Do not leave pet food outside for extended periods of time. Feed pets indoors if possible. 
• Keep compost and rubbish bin lids firmly secured.
• Pick up any fallen fruit from fruit trees and dispose of in secure and lidded compost or rubbish bin.
• Inform neighbours to be on the look-out for German Wasps to prevent other nearby nest colonies from returning.

How to prevent Wasps in general appearing

• To prevent wasps from entering the house, keep doors and windows shut. Ensure flyscreens are fitted and secure.
• Seal gaps around the house to reduce possible entrance sights for German Wasps and other home pests from entering the home.
• Regularly monitor where potential nesting sites may occur.
• Keep pools covered when not in use to prevent wasps from falling in whilst trying to get a drink.
• Consider companion planting of wasp deterring plants such as eucalyptus (shrub forms), lemongrass, marigolds, mint, pennyroyal, thyme, wormwood (Artemisia sp.). Effectiveness of planting may be limited and vary from species to species, however.