Cherry Slug

Foodplant / open feeder
epiphyllous larva of Caliroa cerasi grazes on leaf of Pyrus
Remarks: season: 6-9
Other: major host/prey

Foodplant / open feeder
epiphyllous larva of Caliroa cerasi grazes on leaf of Prunus
Remarks: season: 6-9
Other: major host/prey

Foodplant / open feeder
epiphyllous larva of Caliroa cerasi grazes on leaf of Cydonia oblonga
Remarks: season: 6-9

Foodplant / open feeder
epiphyllous larva of Caliroa cerasi grazes on leaf of Crataegus
Remarks: season: 6-9

Foodplant / open feeder
epiphyllous larva of Caliroa cerasi grazes on leaf of Mespilus germanica
Remarks: season: 6-9

Foodplant / open feeder
epiphyllous larva of Caliroa cerasi grazes on leaf of Quercus
Remarks: season: 6-9

Foodplant / open feeder
epiphyllous larva of Caliroa cerasi grazes on leaf of Rosa
Remarks: season: 6-9

Foodplant / open feeder
epiphyllous larva of Caliroa cerasi grazes on leaf of Rubus
Remarks: season: 6-9

Foodplant / open feeder
epiphyllous larva of Caliroa cerasi grazes on leaf of Salix
Remarks: season: 6-9

Foodplant / open feeder
epiphyllous larva of Caliroa cerasi grazes on leaf of Sorbus
Remarks: season: 6-9

Foodplant / open feeder
epiphyllous larva of Caliroa cerasi grazes on leaf of Prunus avium cv
Remarks: season: 6-9

Foodplant / open feeder
epiphyllous larva of Caliroa cerasi grazes on leaf of Prunus amygdalus
Remarks: season: 6-9

Foodplant / open feeder
epiphyllous larva of Caliroa cerasi grazes on leaf of Sorbus aucuparia
Remarks: season: 6-9

Not of concern, a pest of ornamental and horticulture stock throughout its range.

In Canada adults emerge and fly in mid-June to late July, elsewhere as early as mid-May.

European native, introduced to; North America, Eurasia, Africa, Argentina, Chile, Uraguay, Australia, Tasmania, New Zealand, China.

"Adults: Black sawflies approx. 5.0 mm long. Front and middle tibia brownish. Antenna segment 3 shorter in length than segment 4 + 5. All sawflies of this group posses an ovipositor modified to be used as a saw to facilitate the deposition of eggs under the surface of leaves. Lancet (saw portion of ovipositor) with 17 serrulae (teeth), each long and pointed at apex. Larvae: Small, black and slug-like in appearance, approx. 1.0 mm long at hatch, 11.0 mm long at pupation. Feed on the upper and lower surfaces of leaves. 6 or 7 instars. Dark brown or black head capsule in later instars. Covered with black slime. Pupae: Forms underground within a cocoon constructed of silk and soil. Adapted from descriptions in Smith 1971 and Goulet 1992."

Unknown for adults, larva found on ornamental and horticulture species of the Rosaceae.

Caliroa cerasi overwinters as a pupae, upon emergence females fly to hosts and deposit eggs under the leaf surface. Using the sawlike ovipositor females insert eggs into the leaf from below near the mid-rib or a main vein. After hatching larvae feed on the upper and lower surface of leaves. Larvae are external feeders and skeletonize the host, leaving the vascular structures of leaves intact during feeding. Larval development takes approximately three weeks after which the final instar larvae drop to the ground where they overwinter in the soil. In Canada only one generation per year is produced but in other areas two generations may occur, the second generation emerging a few weeks after the first has finished feeding. Adults can be distinguished from other members of the genus by black slime encapsulating the later larval instars and the all-black legs, other species of Caliroa have some white on the legs. The species is parthenogenic in North America, males are rare in Europe. Caliroa cerasi is likely European in origin and introduced to Canada and elsewhere by commerce. In horticulture stock damage caused to trees by larval feeding can reduce fruit yield and even kill young trees. In ornamental stock damage is considered aesthetically displeasing.

Larvae are cosmopolitan feeders on hosts in the Rosaceae; especially Pyrus (Pear) and Prunus (Cherry); also Cotoneaster, Crataegus (Hawthorn), Chaenomeles and Cydonia, may also feed on Sorbus (Mountain Ash). In North America also recorded from the Aceracea on Acer (Maple) and the Rhamnaceae on Ceanothus.

The pear slug or cherry slug is the larva of the sawfly, Caliroa cerasi, a nearly worldwide pest. The species was first described by Carl Linnaeus in his landmark 1758 10th edition of Systema Naturae. They are not slugs but are a kind of sawfly of the family Tenthredinidae. The pear slug is an important pest that eats leaves of cherry, pear, and plum trees, leaving behind a skeleton of veins. The larvae cover themselves in green slime, making themselves unpalatable to predators. The larva molt between five and eight times before being fully grown. When the larvae are fully grown, they drop from the tree to the ground and pupate underground. The adult sawfly emerges from the pupal case and climbs from the soil to mate and lays eggs on the leaves of the host plant, completing the life cycle.

Other sources dispute the notion that the females climb the tree to lay their eggs, claiming instead that they fly to the tree. This is an important detail in regard to their control in horticultural circumstances where glues are used to control climbing pests.

Pear slug larva on a plum tree