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What's so bad about the spotted lanternfly?
Spotted lanternflies have been hitchhiking their way across Asia and the United States for several years. But why do they keep hitting the headlines?
An invasion of spotted lanternflies (Lycorma delicatula) may not sound as intimidating as that of the honeybee-munching 'murder hornets' that filled social media feeds in 2020, but their ability to swiftly disperse across new ranges is as concerning.
If their spread into new areas isn't controlled, these insects can cause significant damage to both native and economically important plants.
What is a spotted lanternfly?
With their wings outspread, the spotted lanternfly could be mistaken for a colourful butterfly or moth, but they are actually a species of planthopper.
Planthoppers are what entomologists also call 'true bugs' (meaning they are part of the order Hemiptera) and there are about 12,500 species of them found around the world. As their name suggests, they live and feed on plants and they are strong jumpers.
Spotted lanternflies are native to China. They've also been found in adjacent countries in Asia, including South Korea and Japan, but researchers think that it is highly likely that the insects have spread into these areas from China.
During their life cycle, spotted lanternflies go through four wingless stages of growth (known as instars) before becoming adults. In the first three instars after hatching, the tiny nymphs are black with white spots. In the fourth they become red and black with white spots and are about 1.5 centimetres long.
Spotted lanternflies go through four stages of growth. In the fourth instar they are bright red and black with white spots © zhengzaishuru/ Shutterstock
They experience a significant change in appearance when they transform into winged adults. At this stage they are about 2.5 centimetres long and have light grey-brown forewings covered in dark spots. When startled or preparing to take flight they reveal their hindwings which are a striking scarlet with black and white patches. Their abdomens are yellow with black bands.
This species is univoltine, meaning that a generation lasts for one year. Spotted lanternflies hatch in May and are active until December with their eggs surviving through the winter into the next year.
Where are spotted lanternflies an invasive species?
Spotted lanternflies are considered an invasive species in South Korea and the United States. A species is invasive when it is introduced (often unintentionally by people) to a non-native area and spreads, frequently causing harm to the new environment.
They were first reported as an introduced species in Korea in 1932. However, it's possible that this may have been a misidentification as none were reported again until 2006, when they suddenly became a common sight.
In Japan, the insects may have occurred sporadically since the 1930s, but 2008 saw outbreaks of spotted lanternflies in Ishikawa Prefecture.
In 2014, Berks County in Pennsylvania was the site of the first spotted lanternfly sighting in the United States. Since then they have spread substantially throughout the eastern states year by year, and most recently appeared in the Midwestern state of Kansas in 2021. There have been isolated sightings further west, in Utah, California and Oregon, but these have so far been only of dead individuals.
Adult spotted lanternflies have light grey-brown wings covered in dark spots © cwieders/ Shutterstock
Spotted lanternflies are sap-sucking insects and their spread is potentially detrimental to the health of the plants they feed on in their introduced ranges. Many of these are economically important, such as oaks and black walnut.
Grape vineyards, both in South Korea and the United States, appear to be particularly affected, jeopardising an industry worth billions of dollars. One vineyard in the United States reportedly faced a yield loss of up to 90%.
In Pennsylvania alone, if the spotted lanternfly isn't contained, it's estimated that they could drain the state's economy by up to $324 million (£240 million) each year and cause the loss of 2,800 jobs.
The insects also lack predators in their new ranges, so their population can quicky get out of control. As they are relatively inconspicuous when moving into new areas, often their spread goes unnoticed until too late.
How do spotted lanternflies damage plants?
Spotted lanternflies cause damage to plants by sucking sap, with the waste product of their diet encouraging fungal disease.
The spotted lanternfly's preferred host plant is Ailanthus altissima, also known as the tree of heaven, which has been introduced to numerous countries including South Korea, Japan and the USA, and much of Europe. But the insects aren't fussy. A variety of fruit, ornamental and woody trees are on the menu, as are vines, vegetables, herbs and grains.
Planthoppers produce honeydew. It's a sugary liquid they, aphids and some scale insects excrete. Honeydew is attractive to other insects such as wasps, ants and bees, but can also cause sooty mould to grow on the plant it is deposited on. This is a fungal disease that inhibits the plant's ability to photosynthesise and create the energy it needs to survive and grow. It is particularly problematic where the insects congregate in large numbers to feed.
Spotted lanternflies can congregate on plants in large numbers © Eric Dale/ Shutterstock
How are spotted lanternflies spreading?
In both South Korea and the United States the insects suddenly appeared and spread rapidly.
Adult spotted lanternflies have wings and can fly, but usually only cover short distances. With the unintentional help of people, their eggs are possibly the most mobile stage of their life.
Spotted lanternflies lay masses of 30-50 eggs in one place. These are coated by a waxy mud-coloured substance that dries and cracks, called an ootheca, which can camouflage them very effectively.
These insects tend to lay their eggs on flat surfaces. While they will be laid on immobile objects such trees or fenceposts, any outdoors item, such as furniture, pallets or boats, may be used.
People may then unknowingly transport the eggs into new regions and over long distances. The insect's arrival in the USA may have been as a result of stowaway individuals or eggs in a shipping container, for example.
They are also currently able to multiply unimpeded. In their natural range, spotted lanternfly numbers are thought to be kept under control by native predators, such as parasitic wasps. But there are seemingly fewer predators making an impact on their numbers where they have been introduced.
In the United States, assassin bugs and stink bugs have been seen to attack spotted lanternflies. Photos by members of the public of the planthoppers being preyed on are being analysed, with birds, preying mantises, wasps and spiders among the most frequent predators, but work on this area is ongoing.
More research is needed to understand what predators could help to keep spotted lanternfly numbers under control in the United States © Monocletophat123 via Wikimedia Commons (CC BY-SA 4.0)
While there are lower chances of the spotted lanternfly being able to survive in the UK than other parts of the world should they be introduced, it's a possibility that can't yet be ruled out. Their eggs can survive cold winters but it's not clear how warm summers need to be for the insects to complete their life cycle. Their preferred host plant A. altissima is also present in the UK, particularly in east and south-east England.
Are spotted lanternflies dangerous?
Spotted lanternflies are not physically dangerous to humans. They cannot bite as they have only specialised sap-sucking mouthparts.
There have been some suggestions that the insects might be toxic to pets. Currently there is no evidence to support these claims, but more research is needed in this area.
Spotted lanternflies have mouthparts that are specially adapted for slurping plant sap © USGS Bee Inventory and Monitoring Lab via Flickr (Public Domain)
What to do if you see a spotted lanternfly in the United States
Spotted lanternflies are present in multiple states, and each has its own method for managing reports of sightings. The US Department of Agriculture (USDA) list reporting information for each state affected.
If you are outside a zone where the spotted lanternfly is known to be present and see one, it's important that you contact your state agricultural department for advice.
There are several actions individuals can take, including checking your vehicle and items being moved for the insects and their eggs, removing their preferred host tree and where possible parking away from trees with your windows closed, particularly in areas where spotted lanternflies are known to be present.
The USDA advises that live insects and their eggs are removed and destroyed to prevent further spread and damage.
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