Plant Parasites of Europe

leafminers, galls and fungi

Frequently Asked Questions

Parasite or saprophage?

This website discusses parasites, excluding saprophages. In most cases, the distinction between these two is simple: parasites complete their development at the expense of living tissue, while saprophages utilize dead tissue. However, there may be situations where (part of) a living plant is affected, resulting in its death, after which the assailant completes its development in the freshly dead tissue. Parasites also sometimes preferentially exploit weakened or dying tissues, which are already dead by the time they pupate. This is not an exceptional situation, especially in wood-boring beetles, but also in fungi.

Because the literature often does not provide sufficient information on this point, the website sometimes lists species that should not be unequivocally classified as parasites.

Why are gall-mite galls so problematic?

The identification of galls that are induced by gall mines often leads to an unsatisfactory result. Sometimes the descriptions are partly incorrect, or overlapping, the nomenclature my be confusing and incongruous with other publications.

The causers of these galls measure 0.2 mm or less, are hardly visible with the naked eye. Identification is possible only by means of high power microscopes and carefully made preparations. Identification of a gall therefore boils down to the identification of a symptom: confirmation of the identification at the inducer is effectively impossible.

An additional difficulty is that the reaction of the plant is dependent on the size of the mite population. The same species of mite may be asymptomatic in one situation, may cause local silvering of a leaf in another, and at high densities may cause necrotic spots, and even curling of the leaves.

The galls of many of the most common European plants (Acer, Alnus, Betula, Prunus, Salix….) have been studied, and their causers named, around 1900, or earlier. After that period a long-time stagnation followed. All modern literature about the galls consists of a repetition and interpretation of what was seen, or better, could be seen, more than a century ago. The waiting is for an acarologist who is willing to repair this situation.

What is the meaning of the literature references?

They list the sources upon which the description is based. It certainly does not pretend to give an exhaustive list of the literature about the species in question.

Why is “my” plant not mentioned?

Almost always because the plant is discussed in the site is under a more modern name. For practically each scientific plant name there exist a number of synonyms. It is not possible to incorporate them into the site. As far as possible the botanical nomenclature in the site adheres to the Euro+Med PlantBase, and with a check there most of the times the current name of the plant is easily found. If this approach fails (ornamental plants, hybrids) often The Plant List brings a solution.
But as a matter of fact, not any plant that grows in Europe is discussed. Greenhouse plants, indoor ornamentals, uncommon ornamentals, exotics on botanical gardens, and cultivars are not dealt with.

Where can I find the old website

The old website is available on Please note that this website has not been maintained since 2017.