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New England Blade – Olga Kostromytska

Crane flies are relatively common insects, especially in wet or waterlogged areas. They’re also known as “mosquito hawks,” “mosquito killers,” or “giant mosquitos” because at first glance look very similar to mosquitoes. For the most part they are harmless and have no economic or medical significance. Larvae of native species often live in wet, even water-logged, areas and can feed on decaying organic matter.

However, larvae of two invasive species – European crane flies (T. paludosa) and common or marsh crane flies (T. oleracea) can cause serious damage to turfgrasses.  Both species are originally from Europe, where their larvae has been reported as damaging to turfgrass, pasture grass, seedlings in nurseries and many other crops. In the northeastern United States, European crane flies were detected earlier than common crane flies and the species biology and management have been extensively studied. Common crane fly is the less studied species, but recently, it has been reported as damaging or nuisance throughout the region more often than European crane fly (confirmed populations in southeastern, eastern and western Massachusetts, northern Connecticut). According to the recent reports, this species seems to be spreading and the infestations at some locations have intensified in the past few years. Very wet soils are the key factor for crane fly egg and larvae survival. Two years of wet springs and a wet fall in 2019 favored crane flies infestations. If the same trend of weather conditions persist, crane flies will likely to become a reoccurring and a serious problem for turf.

Damage caused by both invasive species is often underestimated and misdiagnosed. On the higher cuts, crane flies cause mostly thinning of the grass and some dead patches. This type of damage is very general and is easy to attribute to factors other than crane flies (such as drought, shade, other insects, etc.). On shorter grass, crane fly damage looks like ball marks, very similar to black cutworm damage.

Common crane fly is potentially the more damaging species because it has two generations per year, larvae are present and can feed throughout the year, with most severe damage in the fall. Often damage caused by common crane flies intensifies after aerification, which has not been noticed for European crane flies. European crane fly has only one generation per year, its larvae are more sensitive to hot summer temperatures and do not actively feed in the summer. European crane flies’ larvae can become a nuisance when they aggregate on the surface in large numbers, which has never been reported for common crane flies. Adults of both species can become a nuisance during the fall flight. Only common crane fly adults fly in the spring (end of April – mid May).

It is important to be on the lookout, understand the invasive crane flies damaging potential to turfgrass and recognize the species predominant in the area. If you suspect a crane fly infestation, please send us a sample or pictures and let us know WHERE and when you saw them (we are trying to get a better understanding of both species’ distribution in the region).

Olga Kostromytska is an Extension Assistant Professor with a specialty in turf entomology at the University of Massachusetts.  Reach her via email at okstromytsk@Umass.educ.