Large-Scale Appearance Of Cobweb-Like Material During The War In Croatia In 1991

by F. Plavsic, Zagreb Clinical Hospital
P. Gotovac, M. Zlatar, MOD Croatia
R. Fuchs, B. Sostaric, MOS Croatia


Widespread appearances of a cobweb-like material over a part of the Croatian territory (Figure 1) during the war in 1991 induced considerable agitation of the population, occasionally even to the verge of a panic reaction. This material also was of high interest to Croatian scientists (1-4). The phenomenon also created interest in diplomatic and other groups from some foreign countries. During the war, the Croatian Medical Headquarters acted to reduce the hysteria and panic reactions of the population. Subsquent to the war, scientific endeavors mainly focused on identifying and explaining the cobweb phenomenon. There was concern that the material might be used as a carrier of chemical or biological warfare agents. However, to date no positive evidence has been obtained that offers a definite explanation of the phenomenon. This report describes the results of examinations of the cobweb material.

Frequency of cobweb appearance

The appearance of cobweb material was most frequent during the autumn 1991, but reports were also received after 1991, in fact in the autumn of each year until today. These are summarized in Table 1. One of the reports was obtained in spring 1992. Most reports were confirmed by military and police authorities, and in many cases, samples of the cobweb material were collected by experts of the Toxicologic Service, Medical Headquarters of Croatia. Sometime at the beginning of November 1991, cobweb-like material appeared in the besieged town of Vukovar. Although the phenomenon was noted, the defenders did not pursue an investigation because of the very difficult situation on the battlefield. Newspapers in Slovenia published data on cobweb contamination of areas near the Croatian border in October 1991, but we have not received the results of investigations from Slovenia.

Simultaneous appearance of spiders and cobweb

A simultaneous appearance of both spiders and cobweb-like material was observed during the first days of November 1991 in the following areas: Komletinci (a village east from Vinkovci, November 3), area between Cakovec and Durdevac in west Slavonia (November 7) and in the whole Zagreb area (November 8). Spiders were collected and identified by experts from the School of Science and Museum of Natural Sciences from Zagreb as domestic species, which regularly migrate from moist regions within Croatia every autumn.

Weather conditions during the appearance of cobweb

Cobweb-like material appeared every year during the stable, hot, rainless and windless autumn period (end of October or beginning of November). Usually, the material appeared during daylight, between 11.00 AM and 4.00 PM., independent of wind directions.

Cobweb appearance in relation to flights of Serbian Air Forces

Some reports from 1991 suggested a relationship between the flights of Serbian Air Forces and appearance of cobweb-like material. However after 1991, Serbian Air Forces did not fly over Croatian territory. A flight of a white, undefined airplane was reported in the case of cobweb appearance over the town of Koprivnica in autumn 1993. According to the reports from 1991, cobweb-like material usually appeared 15 min to 2 h after the flight of Serbian Air Forces. A direct correlation between the flights and appearance of cobweb was recorded in the following four cases: (1) Jastrebarsko at the end of October 1991, when an eyewitness saw a formless object in the sky, just after the flight of a Serbian aircraft. The object descended slowly and spread a cloud composed of cobweb like material; (2) Komletinci on November 3, 1991, when Croatian soldiers saw a parachute-like object in the sky, just after the flight of a Serbian aircraft. The object disintegrated into a cloud of cobweb; (3) Osijek on November 7, 1991, a ball-shaped object appeared in the sky just after the flight of a Serbian aircraft. In a moment, the falling object expanded into a spindle and then disintegrated into a cloud of cobweb (taken on video); (4) Varazdin on November 7, 1991, a Croatian soldier observed cobweb dispersion from the wings of a Serbian aircraft at the moment when the aircraft had finished a missile attack and started rising. In follow-up interviews, eyewitnesses described two other cases of cobweb appearance, each just prior to or after missile attacks. During the autumn 1991, Serbian aircraft flew over the Croatian territory almost every day. In most cases, it was impossible to find a clear relationship between the flights of aircraft and cobweb appearance, particularly on November 7 and November 8, 1991, when the whole territory in the north and east of Croatia was contaminated with cobwebs.

Description of descending and spreading of cobweb material

In most cases, the cobweb-like material is described as a slowly descending cloud, falling to the ground in the form of snowballs, completely or partially unrolled into the constituent fibers. The fresh cobweb material was very sticky and it stuck to all objects on the ground, including trees, houses, cars, people, etc. The cobweb descended at a very slow rate of ²1 m/s. The size of the cloud was never determined. In an estimate made on October 24, 1991 in the town of Kutina, the cobweb cloud was assessed to measure more than 2 km. On November 11, 1991, a cobweb cloud was detected over the entire territory of Slavonia. The density of the cobweb material while in the air was very low. Thus, 200 fibers or snowballs weighed only 80 mg. Upon reaching the ground, the cobweb snowballs or fibers was averaged 2-3 m2. The process of sedimentation from the cloud took about 2-4 h. The cobweb material was found to very quickly lose its sticky feature.

Results of microbiological examinations

The cobweb-like material collected under sterile conditions was sterile. The samples collected in field conditions with unsterile tools were contaminated with microorganisms from the environment, usually with E. coli. Pathogenic bacteria or viruses were never detected in the collected cobweb material.

Detection of chemicals potentially adsorbed on cobweb fibers

Analyses of chemicals potentially adsorbed to cobweb fibers were performed with coupled GC-mass spectrometry systems after extraction with organic solvent. The extracts contained no small organic molecules. Particular attention was paid to chemical weapons and pesticides, but results of the analyses were negative.

Chemical analyses of cobweb fibers

Chemical analyses included the following methods: determination of physical properties of the cobweb (melting point, products of pyrolysis, etc.); total hydrolysis and product analysis; elemental analyses; and IR and Raman spectroscopy. The analyses were performed at two Croatian scientific institutions, and compared with natural, home-collected spider web. According to the chemical analyses, the collected cobweb material was a protein with a structure similar to the natural spider web collected from houses. The IR and Raman spectra of the collected cobweb did not differ from the natural spider web and elemental analyses verified a protein composition typical of spider webs. Results of other analyses The collected cobweb material was composed of basic fibers of 0.1 and 0.4 Ėm in diameter. Microscopic analyses proved the arrangement of basic fibers into coaxial cables. The cobweb fibers were reasonable insulators with a dielectric constant exceeding 4.

Effect of cobweb appearance on Croatian population

The appearance of cobweb-like material during the war in 1991 induced agitation and panic reactions in the population. Because of the Serbian Air Forces frequent flights, people watched the sky very intently and observed many natural phenomena and other events that are usually unobserved in peacetime. During the postwar years, the cobweb appearance was only observed by experts of the Toxicologic Service. Terrified by the experienced war atrocities, most people were inclined to consider the appearance of cobweb in autumn 1991 as a new sign of war escalation. Only the persuasive explanation of Medical Headquarters prevented mass hysteria. The Serbian forces quickly took advantage of these panic reactions of the Croatian people by dropping various materials from their aircraft, e.g., silica, leaves, etc.


Because of the concern of Croatian people to the appearance of these airborne cobwebs during the autumn 1991, the Croatian Medical Headquarters immediately initiated very intensive investigations of the phenomenon. Concurrently, experts from the Toxicologic Service of the Medical Headquarters tried to mitigate hysteria in the population. Two groups of researchers were formed to test two different hypotheses. One group based their investigations on the thesis the cobweb material was a powerful weapon with potentially great effects on human health/environment. The second group tested several theories from 1991 to the present. Their last thesis was that the cobweb appearance was a natural phenomenon, although some facts remain unexplained or only partly explained (e.g., the possible release of cobwebs from Serbian aircraft). Those advocating the first theory point out the following: In some cases, the eyewitnesses saw the appearance of cobweb material just after the flight of Serbian aircraft; release of the material from the aircraft was observed in two or more cases. The cobweb fibers have an extremely large surface, which is a very good property for the potential adsorption of chemical or biological weapons. Due to the high dielectric constant of cobweb fibers and their possible property of diffraction of different rays, the material could be a weapon intended to baffle radars or antiaircraft missiles.
However, these arguments were relatively weak, because:

On the other hand, this group of investigators considering the cobweb a natural phenomenon could not explain the reports of eyewitnesses on cobweb dropping from Serbian aircraft. No matter the final explanation, the appearance of cobweb in 1991 did cause panic reactions in the population of Croatia. During a war, any unexplained event may be the reason for hysteria.


  1. Plavsic F, Petrovecki M, Fuchs R, Sostaric B, Wolf-Coporda A, Bairusi D, Ivicic N, Romic Z, Prlic I. Chemical and ecological aspects of war against Croatia. Croat. Med J 1992;33 (War Suppl): 220-224.
  2. Fuchs R, Sostaric B, Plavsic F, Prodan I, Binenfeld Z. Chemical warfare without chemical agents. Proc 4th Int Symp Protection Against Chemical Warfare Agents. National Defence Research Establishment. Stockholm 1992:127-132.
  3. Sostaric B, Fuchs R, Wrischer M. Application of the cobweb from enemy aircrafts - psychological effect or the real danger. Proc Symp Toxicological Service in the Defense of Homeland. Zagreb 1993: 171-177 (Croatian)
  4. Furic K, Ivanda M, Kucar-Kopic J, Mohacek V. About the structure and composition of the cobweb. Proc Symp Toxicological Service in the Defense of Homeland. Zagreb 1993: 183-185 (Croatian).

Note: For Figures and Tables, please contact ASA to order a copy of the ASA Newsletter.


Return to Main

Return to 1997 archives