Currently, serious, well-founded concern among the public and nature conservation authorities in several regions of Germany continues to be caused by the powerful spread of the so-called «oak processionary caterpillar» - a distinct species of caterpillars. 

It is important to clarify that any caterpillar represents the larval stage of butterflies or moths belonging to the order Lepidoptera. At this stage of their life cycle, which is a transitional one, intensive feeding and active growth occur. Their bodies accumulate nutrient reserves that will later be required for metamorphosis («transition») first into a pupa and then into an imago – the adult butterfly or moth. 

Regarding the mentioned caterpillars «oak processionary caterpillar » (Eichen-Prozessionsspinner or Eichenprozessionsspinner) it should be noted that they, during metamorphosis, are an integral part of the formation and emergence of the butterfly with the elaborate name Thaumetopoeaprocessionea (lat.). Essentially – this is an inconspicuous brown butterfly, the size of an ordinary moth, which is sometimes also called the  «oak processionary moth». 

Eichenprozessionsspinner belongs to the group «processionary caterpillars», which are characterized by an interesting behavioral trait: the caterpillars migrate in long slender columns («processions»), lining up one after another in search of food resources. This, in fact, is what gave them their name.  

They also «build» large, silky nests on trunks and branches of trees. These nests, resembling dense cocoons, serve as their daytime refuge, and at night they go out to feed. The caterpillars' ability to reproduce quickly and their resilience to adverse weather conditions contribute to an increase in their population, which leads to large-scale infestations. And, most sadly, the primary food for caterpillars of this species is oaks. In cases of mass reproduction, they can completely strip a tree of its foliage, leaving only bare branches, which inevitably leads to its weakening.

However, the danger of the «oak processionary caterpillar» is due not so much to its voracity as to the poisonous hairs of the caterpillar (length 0.1 – 0.2 mm, numbering up to 600,000 on each). These microscopic hairs cause strong allergic reactions in humans and animals, manifested by itching, redness, rashes and blisters on the skin.  

When inhaled they irritate the airways, causing coughing and difficulty breathing. Upon contact with the skin, mucous membranes, eyes or respiratory tract they can cause hives, intense itching, conjunctivitis, asthma attacks, and in rare cases – suffocation and anaphylactic shock.

The hairs remain dangerous even after the caterpillars have transformed into butterflies: the wind carries them tens of meters from the silk nests on oaks. It should be remembered that children, the elderly and immunocompromised people are, in this case, in a higher-risk group. 

A few practical tips in this regard: 

Clothing and items: it is important to thoroughly clean (wash) all items that may have come into contact with the caterpillar hairs to avoid further exposure.

Personal hygiene: to completely remove possible remaining hairs, take a shower, paying special attention to washing the entire body and hair.  

Medical assistance: in case of an allergic skin reaction or breathing difficulties, seek qualified medical help immediately.  

Removal of hairs: if caterpillar hairs are found on the skin, they can be carefully removed using adhesive tape.

It is clear that at present a variety of methods are used to reduce the hazard posed by the «oak processionary caterpillar». Among the most common existing practices are, in particular: biological, chemical, mechanical. All of them require appropriately trained specialists and additional financial expenditure.  

Administrations of all 12 administrative districts of Berlin have acknowledged that they are unable to cope in the «battle» with Prozessionsspinner. The reasons are prosaic: lack of personnel and necessary resources. At the same time they express concern that each district of Berlin is forced to act in isolation, developing individual strategies, engaging their own contractors and establishing unique workflows. In their view, such a decentralized approach is ineffective for addressing a citywide problem and requires a unified, coordinated solution, including in the area of financing. 

It appears that in the very near future this topic will become the subject of serious discussion involving the relevant Senate administrations of Berlin, district administrative structures, ecologists and representatives of the healthcare system.