Adult male and female European earwigs (Forficula auricularia) on a flower. Photo courtesy of Whitney Cranshaw, Colorado State University, Bugwood.org.

By Robert Orpet, PhD

Robert Orpet

The European earwig (Forficula auricularia) may be difficult to appreciate because it is an invasive species with menacing rear-pincers, and the name “earwig” is creepy. However, what role do they play in agricultural settings like orchards? Among orchardists interviewed in Central Washington, some believed earwigs to be apple-damaging pests, and others considered them to be aphid predators, but the majority were unsure of the role earwigs play in the orchard ecosystem.

To address this uncertainty, several experiments were designed and literature was reviewed to write a profile article published today in the open-access Journal of Integrated Pest Management about European earwig biology and management in fruit crops. The conclusion: The European earwig is an underappreciated biological control agent and likely a beneficial insect in most apple orchards.

Menacing Pest?

European earwigs are commonly found on damaged apples, but the question arises: Did earwigs cause the damage, or are they merely sheltering in existing damage because of their preference to aggregate in tight spaces? This question was addressed by assessing fruit damage in control plots compared to plots where thousands of earwigs were released. Occasionally earwigs were recovered inside stem bowl splits of apples (see image below), but stem bowl splits are a horticultural issue common to many fruits (such as tomatoes) and are not caused by insect feeding. Earwigs may exploit this damage for food or shelter, but earwigs do not cause of stem bowl spits. Earwigs do occasionally damage apples when confined with them in the lab, but in field conditions, there was no correlation between fruit damage with earwig densities. In relatively soft fruit like peaches, earwigs are pests, but apples may be too hard for earwigs to easily attack.

The European earwig (Forficula auricularia) has been incorrectly associated with apple damage. Stem bowl splits (a) are a horticultural issue; though these splits are sometimes chewed on by earwigs (b, upper arrow) and sheltered in by earwigs (b, lower arrow). Earwigs have been observed to cause damage to apples during laboratory confinement, but field studies have shown no correlation between fruit damage and earwig densities. (Image originally published in Orpet et al. 2019, Journal of Integrated Pest Management)

Friendly Predator?

Unlike popular and celebrated predators like lady beetles, European earwigs are nocturnal, which makes it difficult for apple orchard managers to observe and appreciate their biological control services. To obtain direct evidence of predatory behavior, video footage was captured of earwigs consuming a woolly apple aphid (Eriosoma lanigerum) colony at night.

Earwigs are generalist predators, capable of eating a variety of insect pests, and experimental evidence shows European earwigs contribute to woolly apple aphid and green apple aphid (Aphis pomi) suppression. More research is needed to assess their importance in suppressing other pests across crop systems.

A Multifaceted and Charismatic Insect

European earwigs are notable not only for their economic importance but also for their intriguing combination of unexpected, mysterious, and endearing behaviors. For example, despite their tough image and forceps-like pincers for defense, European earwigs quickly retreat after contact with small ants in the field, hence avoiding potentially life-threatening conflicts. Most endearingly, females practice maternal care during their nesting phase over winter. They keep their eggs and nymphs safe from fungi and nest-invaders and provision them with food (see image below).

European earwig (Forficula auricularia) nests with eggs (a) and nymphs (b) were found underneath a concrete block on the grounds of Washington State University Tree Fruit Research and Extension Center on April 23 (photo by Lukas Sherman) and April 27, 2019, respectively. (Photo credits: (a) Lukas Sherman, (b) Robert Orpet, Ph.D. Image originally published in Orpet et al. 2019, Journal of Integrated Pest Management)

Sharing earwig behavior with apple growers might help improve the image of these charismatic and potentially beneficial insects. So, while they are not likeable in all aspects, the European earwigs are indeed fascinating and economically important animals.

Robert Orpet, Ph.D., is an entomologist in Dr. Louis Nottingham’s tree fruit research group at Washington State University’s Tree Fruit Research and Extension Center. Orpet obtained a Ph.D. in entomology in December 2018 under Drs. Vince Jones and Dave Crowder. Email: robert.orpet@wsu.edu. Washington Tree Fruit Research Commission and Western SARE provided funding to support the work described in this article.